diff --git a/fastNLP/__init__.py b/fastNLP/__init__.py
index c67e5919..e666f65f 100644
--- a/fastNLP/__init__.py
+++ b/fastNLP/__init__.py
@@ -12,7 +12,11 @@ fastNLP 中最常用的组件可以直接从 fastNLP 包中 import ，他们的
 __all__ = [
     "Instance",
     "FieldArray",
-    "Batch",
+
+    "DataSetIter",
+    "BatchIter",
+    "TorchLoaderIter",
+
     "Vocabulary",
     "DataSet",
     "Const",
diff --git a/fastNLP/core/__init__.py b/fastNLP/core/__init__.py
index d6ab8983..792bff66 100644
--- a/fastNLP/core/__init__.py
+++ b/fastNLP/core/__init__.py
@@ -14,7 +14,7 @@ core 模块里实现了 fastNLP 的核心框架，常用的功能都可以从 fa
     介绍core 的子模块的分工，好像必要性不大
     
 """
-from .batch import Batch
+from .batch import DataSetIter, BatchIter, TorchLoaderIter
 from .callback import Callback, GradientClipCallback, EarlyStopCallback, TensorboardCallback, LRScheduler, ControlC
 from .const import Const
 from .dataset import DataSet
diff --git a/fastNLP/core/batch.py b/fastNLP/core/batch.py
index 0ca920d4..89b55a25 100644
--- a/fastNLP/core/batch.py
+++ b/fastNLP/core/batch.py
@@ -3,7 +3,9 @@ batch 模块实现了 fastNLP 所需的 Batch 类。
 
 """
 __all__ = [
-    "Batch"
+    "BatchIter",
+    "DataSetIter",
+    "TorchLoaderIter",
 ]
 
 import atexit
@@ -12,9 +14,11 @@ from queue import Empty, Full
 import numpy as np
 import torch
 import torch.multiprocessing as mp
+import torch.utils.data
 from numbers import Number
 
-from .sampler import RandomSampler
+from .sampler import SequentialSampler
+from .dataset import DataSet
 
 _python_is_exit = False
 
@@ -27,162 +31,157 @@ def _set_python_is_exit():
 atexit.register(_set_python_is_exit)
 
 
-class Batch(object):
-    """
-    别名：:class:`fastNLP.Batch` :class:`fastNLP.core.batch.Batch`
-
-    Batch 用于从 `DataSet` 中按一定的顺序, 依次按 ``batch_size`` 的大小将数据取出，
-    组成 `x` 和 `y`::
-
-        batch = Batch(data_set, batch_size=16, sampler=SequentialSampler())
-        num_batch = len(batch)
-        for batch_x, batch_y in batch:
-            # do stuff ...
-
-    :param dataset: :class:`~fastNLP.DataSet` 对象, 数据集
-    :param int batch_size: 取出的batch大小
-    :param sampler: 规定使用的 :class:`~fastNLP.Sampler` 方式. 若为 ``None`` , 使用 :class:`~fastNLP.RandomSampler`.
-    
-        Default: ``None``
-    :param bool as_numpy: 若为 ``True`` , 输出batch为 numpy.array. 否则为 :class:`torch.Tensor`.
-    
-        Default: ``False``
-    :param bool prefetch: 若为 ``True`` 使用多进程预先取出下一batch.
-    
-        Default: ``False``
-    """
-    
-    def __init__(self, dataset, batch_size, sampler=None, as_numpy=False, prefetch=False):
+class DataSetGetter:
+    def __init__(self, dataset: DataSet, as_numpy=False):
         self.dataset = dataset
-        self.batch_size = batch_size
-        if sampler is None:
-            sampler = RandomSampler()
-        self.sampler = sampler
+        self.inputs = {n: f for n, f in dataset.get_all_fields().items() if f.is_input}
+        self.targets = {n: f for n, f in dataset.get_all_fields().items() if f.is_target}
         self.as_numpy = as_numpy
-        self.idx_list = None
-        self.curidx = 0
-        self.num_batches = len(dataset) // batch_size + int(len(dataset) % batch_size != 0)
-        self.cur_batch_indices = None
-        self.prefetch = prefetch
-        self.lengths = 0
-    
-    def fetch_one(self):
-        if self.curidx >= len(self.idx_list):
-            return None
+        self.idx_list = list(range(len(dataset)))
+
+    def __getitem__(self, idx: int):
+        # mapping idx to sampled idx
+        idx = self.idx_list[idx]
+        inputs = {n:f.get(idx) for n, f in self.inputs.items()}
+        targets = {n:f.get(idx) for n, f in self.targets.items()}
+        return idx, inputs, targets
+
+    def __len__(self):
+        return len(self.dataset)
+
+    def collate_fn(self, batch: list):
+        batch_x = {n:[] for n in self.inputs.keys()}
+        batch_y = {n:[] for n in self.targets.keys()}
+        indices = []
+        for idx, x, y in batch:
+            indices.append(idx)
+            for n, v in x.items():
+                batch_x[n].append(v)
+            for n, v in y.items():
+                batch_y[n].append(v)
+
+        def pad_batch(batch_dict, field_array):
+            for n, vlist in batch_dict.items():
+                f = field_array[n]
+                if f.padder is None:
+                    batch_dict[n] = np.array(vlist)
+                else:
+                    data = f.pad(vlist)
+                    if not self.as_numpy:
+                        data, flag = _to_tensor(data, f.dtype)
+                    batch_dict[n] = data
+            return batch_dict
+
+        return (indices,
+                pad_batch(batch_x, self.inputs),
+                pad_batch(batch_y, self.targets))
+
+    def set_idx_list(self, idx_list):
+        if len(idx_list) != len(self.idx_list):
+            raise ValueError
+        self.idx_list = idx_list
+
+    def __getattr__(self, item):
+        if hasattr(self.dataset, item):
+            return getattr(self.dataset, item)
         else:
-            endidx = min(self.curidx + self.batch_size, len(self.idx_list))
-            batch_x, batch_y = {}, {}
-            
-            indices = self.idx_list[self.curidx:endidx]
-            self.cur_batch_indices = indices
-            
-            for field_name, field in self.dataset.get_all_fields().items():
-                if field.is_target or field.is_input:
-                    batch = field.get(indices)
-                    if not self.as_numpy and \
-                            field.dtype is not None and \
-                                issubclass(field.dtype, Number) and not isinstance(batch, torch.Tensor):
-                        batch = _to_tensor(batch)
-                    if field.is_target:
-                        batch_y[field_name] = batch
-                    if field.is_input:
-                        batch_x[field_name] = batch
-            
-            self.curidx = endidx
-            return batch_x, batch_y
-    
+            raise AttributeError("'DataSetGetter' object has no attribute '{}'".format(item))
+
+
+class SamplerAdapter(torch.utils.data.Sampler):
+    def __init__(self, sampler, dataset):
+        self.sampler = sampler
+        self.dataset = dataset
+
     def __iter__(self):
-        """
-        Iterate on dataset, fetch batch data. Fetch process don't block the iterate process
-        :return:
-        """
-        if self.prefetch:
-            return self._run_batch_iter(self)
-        
-        def batch_iter():
-            self.init_iter()
-            while 1:
-                res = self.fetch_one()
-                if res is None:
-                    break
-                yield res
-        
-        return batch_iter()
-    
+        return iter(self.sampler(self.dataset))
+
+
+class BatchIter:
+    def __init__(self):
+        self.dataiter = None
+        self.num_batches = None
+        self.cur_batch_indices = None
+        self.batch_size = None
+
     def init_iter(self):
-        self.idx_list = self.sampler(self.dataset)
-        self.curidx = 0
-        self.lengths = self.dataset.get_length()
-    
+        pass
+
+    @staticmethod
+    def get_num_batches(num_samples, batch_size, drop_last):
+        num_batches = num_samples // batch_size
+        if not drop_last and (num_samples % batch_size > 0):
+            num_batches += 1
+        return num_batches
+
+    def __iter__(self):
+        self.init_iter()
+        for indices, batch_x, batch_y in self.dataiter:
+            self.cur_batch_indices = indices
+            yield batch_x, batch_y
+
+    def get_batch_indices(self):
+        return self.cur_batch_indices
+
     def __len__(self):
         return self.num_batches
-    
-    def get_batch_indices(self):
-        """
-        取得当前batch在DataSet中所在的index下标序列
 
-        :return list(int) indexes: 下标序列
-        """
-        return self.cur_batch_indices
-    
-    @staticmethod
-    def _run_fetch(batch, q):
-        try:
-            global _python_is_exit
-            batch.init_iter()
-            # print('start fetch')
-            while 1:
-                res = batch.fetch_one()
-                # print('fetch one')
-                while 1:
-                    try:
-                        q.put(res, timeout=3)
-                        break
-                    except Full:
-                        if _python_is_exit:
-                            return
-                if res is None:
-                    # print('fetch done, waiting processing')
-                    break
-            # print('fetch exit')
-        except Exception as e:
-            q.put(e)
-        finally:
-            q.join()
-    
-    @staticmethod
-    def _run_batch_iter(batch):
-        q = mp.JoinableQueue(maxsize=10)
-        fetch_p = mp.Process(target=Batch._run_fetch, args=(batch, q))
-        fetch_p.daemon = True
-        fetch_p.start()
-        # print('fork fetch process')
-        while 1:
-            try:
-                res = q.get(timeout=1)
-                q.task_done()
-                # print('get fetched')
-                if res is None:
-                    break
-                elif isinstance(res, Exception):
-                    raise res
-                yield res
-            except Empty as e:
-                if fetch_p.is_alive():
-                    continue
-                else:
-                    break
-        fetch_p.terminate()
-        fetch_p.join()
-        # print('iter done')
+    @property
+    def dataset(self):
+        return self.dataiter.dataset
+
+
+class DataSetIter(BatchIter):
+    def __init__(self, dataset, batch_size=1, sampler=None, as_numpy=False,
+                 num_workers=0, pin_memory=False, drop_last=False,
+                 timeout=0, worker_init_fn=None):
+        super().__init__()
+        assert isinstance(dataset, DataSet)
+        sampler = SamplerAdapter(sampler=sampler or SequentialSampler(), dataset=dataset)
+        dataset = DataSetGetter(dataset, as_numpy)
+        collate_fn = dataset.collate_fn if hasattr(dataset, 'collate_fn') else None
+        self.dataiter = torch.utils.data.DataLoader(
+            dataset=dataset, batch_size=batch_size, sampler=sampler,
+            collate_fn=collate_fn, num_workers=num_workers,
+            pin_memory=pin_memory, drop_last=drop_last,
+            timeout=timeout, worker_init_fn=worker_init_fn)
+        self.num_batches = self.get_num_batches(len(dataset), batch_size, drop_last)
+        self.batch_size = batch_size
+
+
+class TorchLoaderIter(BatchIter):
+    def __init__(self, dataset):
+        super().__init__()
+        assert isinstance(dataset, torch.utils.data.DataLoader)
+        self.dataiter = dataset
+        self.num_batches = self.get_num_batches(len(dataset), dataset.batch_size, dataset.drop_last)
+        self.batch_size = dataset.batch_size
 
 
-def _to_tensor(batch):
+class OnlineDataGettter:
+    # TODO
+    pass
+
+
+class OnlineDataIter(BatchIter):
+    # TODO
+    def __init__(self, dataset, batch_size=1, buffer_size=10000, sampler=None, as_numpy=False,
+                 num_workers=0, pin_memory=False, drop_last=False,
+                 timeout=0, worker_init_fn=None, **kwargs):
+        super().__init__()
+
+
+def _to_tensor(batch, field_dtype):
     try:
-        if issubclass(batch.dtype.type, np.floating):
-            batch = torch.as_tensor(batch).float()  # 默认使用float32
+        if field_dtype is not None \
+                and issubclass(field_dtype, Number) \
+                and not isinstance(batch, torch.Tensor):
+            if issubclass(batch.dtype.type, np.floating):
+                new_batch = torch.as_tensor(batch).float()  # 默认使用float32
+            else:
+                new_batch = torch.as_tensor(batch)  # 复用内存地址，避免复制
+            return new_batch, True
         else:
-            batch = torch.as_tensor(batch)  # 复用内存地址，避免复制
+            return batch, False
     except:
-        pass
-    return batch
+        return batch, False
diff --git a/fastNLP/core/field.py b/fastNLP/core/field.py
index b0a36765..7dc29ba3 100644
--- a/fastNLP/core/field.py
+++ b/fastNLP/core/field.py
@@ -176,7 +176,10 @@ class FieldArray:
         if self.padder is None or pad is False:
             return np.array(contents)
         else:
-            return self.padder(contents, field_name=self.name, field_ele_dtype=self.dtype, dim=self._cell_ndim)
+            return self.pad(contents)
+
+    def pad(self, contents):
+        return self.padder(contents, field_name=self.name, field_ele_dtype=self.dtype, dim=self._cell_ndim)
 
     def set_padder(self, padder):
         """
diff --git a/fastNLP/core/losses.py b/fastNLP/core/losses.py
index 8b17f75a..66234ce7 100644
--- a/fastNLP/core/losses.py
+++ b/fastNLP/core/losses.py
@@ -34,14 +34,23 @@ class LossBase(object):
     """
     
     def __init__(self):
-        self.param_map = {}
+        self._param_map = {}  # key是fun的参数，value是以该值从传入的dict取出value
         self._checked = False
-    
+
+    @property
+    def param_map(self):
+        if len(self._param_map) == 0:  # 如果为空说明还没有初始化
+            func_spect = inspect.getfullargspec(self.get_loss)
+            func_args = [arg for arg in func_spect.args if arg != 'self']
+            for arg in func_args:
+                self._param_map[arg] = arg
+        return self._param_map
+
     def get_loss(self, *args, **kwargs):
         raise NotImplementedError
     
     def _init_param_map(self, key_map=None, **kwargs):
-        """检查key_map和其他参数map，并将这些映射关系添加到self.param_map
+        """检查key_map和其他参数map，并将这些映射关系添加到self._param_map
 
         :param dict key_map: 表示key的映射关系
         :param kwargs: key word args里面的每一个的键-值对都会被构造成映射关系
@@ -53,30 +62,30 @@ class LossBase(object):
                 raise TypeError("key_map must be `dict`, got {}.".format(type(key_map)))
             for key, value in key_map.items():
                 if value is None:
-                    self.param_map[key] = key
+                    self._param_map[key] = key
                     continue
                 if not isinstance(key, str):
                     raise TypeError(f"key in key_map must be `str`, not `{type(key)}`.")
                 if not isinstance(value, str):
                     raise TypeError(f"value in key_map must be `str`, not `{type(value)}`.")
-                self.param_map[key] = value
+                self._param_map[key] = value
                 value_counter[value].add(key)
         for key, value in kwargs.items():
             if value is None:
-                self.param_map[key] = key
+                self._param_map[key] = key
                 continue
             if not isinstance(value, str):
                 raise TypeError(f"in {key}={value}, value must be `str`, not `{type(value)}`.")
-            self.param_map[key] = value
+            self._param_map[key] = value
             value_counter[value].add(key)
         for value, key_set in value_counter.items():
             if len(key_set) > 1:
                 raise ValueError(f"Several parameters:{key_set} are provided with one output {value}.")
         
-        # check consistence between signature and param_map
+        # check consistence between signature and _param_map
         func_spect = inspect.getfullargspec(self.get_loss)
         func_args = [arg for arg in func_spect.args if arg != 'self']
-        for func_param, input_param in self.param_map.items():
+        for func_param, input_param in self._param_map.items():
             if func_param not in func_args:
                 raise NameError(
                     f"Parameter `{func_param}` is not in {_get_func_signature(self.get_loss)}. Please check the "
@@ -96,7 +105,7 @@ class LossBase(object):
         :return: dict, if dict is not {}, pass it to self.evaluate. Otherwise do mapping.
         """
         fast_param = {}
-        if len(self.param_map) == 2 and len(pred_dict) == 1 and len(target_dict) == 1:
+        if len(self._param_map) == 2 and len(pred_dict) == 1 and len(target_dict) == 1:
             fast_param['pred'] = list(pred_dict.values())[0]
             fast_param['target'] = list(target_dict.values())[0]
             return fast_param
@@ -115,19 +124,19 @@ class LossBase(object):
             return loss
         
         if not self._checked:
-            # 1. check consistence between signature and param_map
+            # 1. check consistence between signature and _param_map
             func_spect = inspect.getfullargspec(self.get_loss)
             func_args = set([arg for arg in func_spect.args if arg != 'self'])
-            for func_arg, input_arg in self.param_map.items():
+            for func_arg, input_arg in self._param_map.items():
                 if func_arg not in func_args:
                     raise NameError(f"`{func_arg}` not in {_get_func_signature(self.get_loss)}.")
             
-            # 2. only part of the param_map are passed, left are not
+            # 2. only part of the _param_map are passed, left are not
             for arg in func_args:
-                if arg not in self.param_map:
-                    self.param_map[arg] = arg  # This param does not need mapping.
+                if arg not in self._param_map:
+                    self._param_map[arg] = arg  # This param does not need mapping.
             self._evaluate_args = func_args
-            self._reverse_param_map = {input_arg: func_arg for func_arg, input_arg in self.param_map.items()}
+            self._reverse_param_map = {input_arg: func_arg for func_arg, input_arg in self._param_map.items()}
 
         mapped_pred_dict = {}
         mapped_target_dict = {}
@@ -149,7 +158,7 @@ class LossBase(object):
             replaced_missing = list(missing)
             for idx, func_arg in enumerate(missing):
                 # Don't delete `` in this information, nor add ``
-                replaced_missing[idx] = f"{self.param_map[func_arg]}" + f"(assign to `{func_arg}` " \
+                replaced_missing[idx] = f"{self._param_map[func_arg]}" + f"(assign to `{func_arg}` " \
                     f"in `{self.__class__.__name__}`)"
             
             check_res = _CheckRes(missing=replaced_missing,
@@ -162,6 +171,8 @@ class LossBase(object):
             if check_res.missing or check_res.duplicated:
                 raise _CheckError(check_res=check_res,
                                   func_signature=_get_func_signature(self.get_loss))
+            self._checked = True
+
         refined_args = _build_args(self.get_loss, **mapped_pred_dict, **mapped_target_dict)
         
         loss = self.get_loss(**refined_args)
diff --git a/fastNLP/core/metrics.py b/fastNLP/core/metrics.py
index 37a94a08..cfcb9039 100644
--- a/fastNLP/core/metrics.py
+++ b/fastNLP/core/metrics.py
@@ -115,9 +115,18 @@ class MetricBase(object):
     """
     
     def __init__(self):
-        self.param_map = {}  # key is param in function, value is input param.
+        self._param_map = {}  # key is param in function, value is input param.
         self._checked = False
 
+    @property
+    def param_map(self):
+        if len(self._param_map) == 0:  # 如果为空说明还没有初始化
+            func_spect = inspect.getfullargspec(self.evaluate)
+            func_args = [arg for arg in func_spect.args if arg != 'self']
+            for arg in func_args:
+                self._param_map[arg] = arg
+        return self._param_map
+
     @abstractmethod
     def evaluate(self, *args, **kwargs):
         raise NotImplementedError
@@ -127,7 +136,7 @@ class MetricBase(object):
         raise NotImplemented
     
     def _init_param_map(self, key_map=None, **kwargs):
-        """检查key_map和其他参数map，并将这些映射关系添加到self.param_map
+        """检查key_map和其他参数map，并将这些映射关系添加到self._param_map
 
         :param dict key_map: 表示key的映射关系
         :param kwargs: key word args里面的每一个的键-值对都会被构造成映射关系
@@ -139,30 +148,30 @@ class MetricBase(object):
                 raise TypeError("key_map must be `dict`, got {}.".format(type(key_map)))
             for key, value in key_map.items():
                 if value is None:
-                    self.param_map[key] = key
+                    self._param_map[key] = key
                     continue
                 if not isinstance(key, str):
                     raise TypeError(f"key in key_map must be `str`, not `{type(key)}`.")
                 if not isinstance(value, str):
                     raise TypeError(f"value in key_map must be `str`, not `{type(value)}`.")
-                self.param_map[key] = value
+                self._param_map[key] = value
                 value_counter[value].add(key)
         for key, value in kwargs.items():
             if value is None:
-                self.param_map[key] = key
+                self._param_map[key] = key
                 continue
             if not isinstance(value, str):
                 raise TypeError(f"in {key}={value}, value must be `str`, not `{type(value)}`.")
-            self.param_map[key] = value
+            self._param_map[key] = value
             value_counter[value].add(key)
         for value, key_set in value_counter.items():
             if len(key_set) > 1:
                 raise ValueError(f"Several parameters:{key_set} are provided with one output {value}.")
         
-        # check consistence between signature and param_map
+        # check consistence between signature and _param_map
         func_spect = inspect.getfullargspec(self.evaluate)
         func_args = [arg for arg in func_spect.args if arg != 'self']
-        for func_param, input_param in self.param_map.items():
+        for func_param, input_param in self._param_map.items():
             if func_param not in func_args:
                 raise NameError(
                     f"Parameter `{func_param}` is not in {_get_func_signature(self.evaluate)}. Please check the "
@@ -177,7 +186,7 @@ class MetricBase(object):
         :return: dict, if dict is not {}, pass it to self.evaluate. Otherwise do mapping.
         """
         fast_param = {}
-        if len(self.param_map) == 2 and len(pred_dict) == 1 and len(target_dict) == 1:
+        if len(self._param_map) == 2 and len(pred_dict) == 1 and len(target_dict) == 1:
             fast_param['pred'] = list(pred_dict.values())[0]
             fast_param['target'] = list(target_dict.values())[0]
             return fast_param
@@ -206,19 +215,19 @@ class MetricBase(object):
         if not self._checked:
             if not callable(self.evaluate):
                 raise TypeError(f"{self.__class__.__name__}.evaluate has to be callable, not {type(self.evaluate)}.")
-            # 1. check consistence between signature and param_map
+            # 1. check consistence between signature and _param_map
             func_spect = inspect.getfullargspec(self.evaluate)
             func_args = set([arg for arg in func_spect.args if arg != 'self'])
-            for func_arg, input_arg in self.param_map.items():
+            for func_arg, input_arg in self._param_map.items():
                 if func_arg not in func_args:
                     raise NameError(f"`{func_arg}` not in {_get_func_signature(self.evaluate)}.")
             
-            # 2. only part of the param_map are passed, left are not
+            # 2. only part of the _param_map are passed, left are not
             for arg in func_args:
-                if arg not in self.param_map:
-                    self.param_map[arg] = arg  # This param does not need mapping.
+                if arg not in self._param_map:
+                    self._param_map[arg] = arg  # This param does not need mapping.
             self._evaluate_args = func_args
-            self._reverse_param_map = {input_arg: func_arg for func_arg, input_arg in self.param_map.items()}
+            self._reverse_param_map = {input_arg: func_arg for func_arg, input_arg in self._param_map.items()}
         
         # need to wrap inputs in dict.
         mapped_pred_dict = {}
@@ -242,7 +251,7 @@ class MetricBase(object):
             replaced_missing = list(missing)
             for idx, func_arg in enumerate(missing):
                 # Don't delete `` in this information, nor add ``
-                replaced_missing[idx] = f"{self.param_map[func_arg]}" + f"(assign to `{func_arg}` " \
+                replaced_missing[idx] = f"{self._param_map[func_arg]}" + f"(assign to `{func_arg}` " \
                     f"in `{self.__class__.__name__}`)"
             
             check_res = _CheckRes(missing=replaced_missing,
@@ -255,10 +264,10 @@ class MetricBase(object):
             if check_res.missing or check_res.duplicated:
                 raise _CheckError(check_res=check_res,
                                   func_signature=_get_func_signature(self.evaluate))
+            self._checked = True
         refined_args = _build_args(self.evaluate, **mapped_pred_dict, **mapped_target_dict)
         
         self.evaluate(**refined_args)
-        self._checked = True
         
         return
 
@@ -416,19 +425,19 @@ def _bioes_tag_to_spans(tags, ignore_labels=None):
     ignore_labels = set(ignore_labels) if ignore_labels else set()
 
     spans = []
-    prev_bmes_tag = None
+    prev_bioes_tag = None
     for idx, tag in enumerate(tags):
         tag = tag.lower()
-        bmes_tag, label = tag[:1], tag[2:]
-        if bmes_tag in ('b', 's'):
+        bieso_tag, label = tag[:1], tag[2:]
+        if bieso_tag in ('b', 's'):
             spans.append((label, [idx, idx]))
-        elif bmes_tag in ('i', 'e') and prev_bmes_tag in ('b', 'i') and label == spans[-1][0]:
+        elif bieso_tag in ('i', 'e') and prev_bioes_tag in ('b', 'i') and label == spans[-1][0]:
             spans[-1][1][1] = idx
-        elif bmes_tag == 'o':
+        elif bieso_tag == 'o':
             pass
         else:
             spans.append((label, [idx, idx]))
-        prev_bmes_tag = bmes_tag
+        prev_bioes_tag = bieso_tag
     return [(span[0], (span[1][0], span[1][1] + 1))
             for span in spans
             if span[0] not in ignore_labels
diff --git a/fastNLP/core/predictor.py b/fastNLP/core/predictor.py
index 4f37e105..06e586c6 100644
--- a/fastNLP/core/predictor.py
+++ b/fastNLP/core/predictor.py
@@ -6,7 +6,7 @@ from collections import defaultdict
 
 import torch
 
-from . import Batch
+from . import DataSetIter
 from . import DataSet
 from . import SequentialSampler
 from .utils import _build_args
@@ -44,8 +44,7 @@ class Predictor(object):
 
         self.network.eval()
         batch_output = defaultdict(list)
-        data_iterator = Batch(data, batch_size=self.batch_size, sampler=SequentialSampler(), as_numpy=False,
-                              prefetch=False)
+        data_iterator = DataSetIter(data, batch_size=self.batch_size, sampler=SequentialSampler(), as_numpy=False)
 
         if hasattr(self.network, "predict"):
             predict_func = self.network.predict
diff --git a/fastNLP/core/tester.py b/fastNLP/core/tester.py
index 883e0d01..398afe6b 100644
--- a/fastNLP/core/tester.py
+++ b/fastNLP/core/tester.py
@@ -37,7 +37,7 @@ import warnings
 import torch
 import torch.nn as nn
 
-from .batch import Batch
+from .batch import BatchIter, DataSetIter
 from .dataset import DataSet
 from .metrics import _prepare_metrics
 from .sampler import SequentialSampler
@@ -82,7 +82,7 @@ class Tester(object):
     :param int verbose: 如果为0不输出任何信息; 如果为1，打印出验证结果。
     """
     
-    def __init__(self, data, model, metrics, batch_size=16, device=None, verbose=1):
+    def __init__(self, data, model, metrics, batch_size=16, num_workers=0, device=None, verbose=1):
         super(Tester, self).__init__()
         
         if not isinstance(data, DataSet):
@@ -96,6 +96,14 @@ class Tester(object):
         self._model = _move_model_to_device(model, device=device)
         self.batch_size = batch_size
         self.verbose = verbose
+
+        if isinstance(data, DataSet):
+            self.data_iterator = DataSetIter(
+                dataset=data, batch_size=batch_size, num_workers=num_workers)
+        elif isinstance(data, BatchIter):
+            self.data_iterator = data
+        else:
+            raise TypeError("data type {} not support".format(type(data)))
         
         #  如果是DataParallel将没有办法使用predict方法
         if isinstance(self._model, nn.DataParallel):
@@ -124,7 +132,7 @@ class Tester(object):
         self._model_device = _get_model_device(self._model)
         network = self._model
         self._mode(network, is_test=True)
-        data_iterator = Batch(self.data, self.batch_size, sampler=SequentialSampler(), as_numpy=False)
+        data_iterator = self.data_iterator
         eval_results = {}
         try:
             with torch.no_grad():
diff --git a/fastNLP/core/trainer.py b/fastNLP/core/trainer.py
index d7694e00..8dece12d 100644
--- a/fastNLP/core/trainer.py
+++ b/fastNLP/core/trainer.py
@@ -311,8 +311,9 @@ try:
     from tqdm.auto import tqdm
 except:
     from .utils import _pseudo_tqdm as tqdm
+import warnings
 
-from .batch import Batch
+from .batch import DataSetIter, BatchIter
 from .callback import CallbackManager, CallbackException
 from .dataset import DataSet
 from .losses import _prepare_losser
@@ -320,7 +321,6 @@ from .metrics import _prepare_metrics
 from .optimizer import Optimizer
 from .sampler import Sampler
 from .sampler import RandomSampler
-from .sampler import SequentialSampler
 from .tester import Tester
 from .utils import _CheckError
 from .utils import _build_args
@@ -351,6 +351,8 @@ class Trainer(object):
     :param int batch_size: 训练和验证的时候的batch大小。
     :param loss: 使用的 :class:`~fastNLP.core.losses.LossBase` 对象。当为None时，默认使用 :class:`~fastNLP.LossInForward`
     :param sampler: Batch数据生成的顺序， :class:`~fastNLP.Sampler` 类型。如果为None，默认使用 :class:`~fastNLP.RandomSampler`
+    :param drop_last: 如果最后一个batch没有正好为batch_size这么多数据，就扔掉最后一个batch
+    :param num_workers: int, 有多少个线程来进行数据pad处理。
     :param update_every: int, 多少步更新一次梯度。用于希望累计梯度的场景，比如需要128的batch_size, 但是直接设为128
         会导致内存不足，通过设置batch_size=32, update_every=4达到目的。当optimizer为None时，该参数无效。
     :param int n_epochs: 需要优化迭代多少次。
@@ -367,7 +369,6 @@ class Trainer(object):
     :param int validate_every: 多少个step在验证集上验证一次; 如果为-1，则每个epoch结束验证一次。仅在传入dev_data时有效。
     :param str,None save_path: 将模型保存路径。如果为None，则不保存模型。如果dev_data为None，则保存最后一次迭代的模型。
         保存的时候不仅保存了参数，还保存了模型结构。即便使用DataParallel，这里也只保存模型。
-    :param prefetch: bool, 是否使用额外的进程对产生batch数据。理论上会使得Batch迭代更快。
     :param bool use_tqdm: 是否使用tqdm来显示训练进度; 如果为False，则将loss打印在终端中。
     :param str,int,torch.device,list(int) device: 将模型load到哪个设备。默认为None，即Trainer不对模型
         的计算位置进行管理。支持以下的输入:
@@ -394,16 +395,17 @@ class Trainer(object):
     """
     
     def __init__(self, train_data, model, optimizer=None, loss=None,
-                 batch_size=32, sampler=None, update_every=1,
-                 n_epochs=10, print_every=5,
+                 batch_size=32, sampler=None, drop_last=False, update_every=1,
+                 num_workers=0, n_epochs=10, print_every=5,
                  dev_data=None, metrics=None, metric_key=None,
-                 validate_every=-1, save_path=None,
-                 prefetch=False, use_tqdm=True, device=None,
-                 callbacks=None,
-                 check_code_level=0):
+                 validate_every=-1, save_path=None, use_tqdm=True, device=None, prefetch=False,
+                 callbacks=None, check_code_level=0):
+        if prefetch and num_workers==0:
+            num_workers = 1
+        if prefetch:
+            warnings.warn("prefetch is deprecated, will be removed in version 0.5.0, please use num_workers instead.")
+
         super(Trainer, self).__init__()
-        if not isinstance(train_data, DataSet):
-            raise TypeError(f"The type of train_data must be fastNLP.DataSet, got {type(train_data)}.")
         if not isinstance(model, nn.Module):
             raise TypeError(f"The type of model must be torch.nn.Module, got {type(model)}.")
         
@@ -430,17 +432,27 @@ class Trainer(object):
         if metric_key is not None:
             self.increase_better = False if metric_key[0] == "-" else True
             self.metric_key = metric_key[1:] if metric_key[0] == "+" or metric_key[0] == "-" else metric_key
-        elif len(metrics) > 0:
-            self.metric_key = metrics[0].__class__.__name__.lower().strip('metric')
-        
+        else:
+            self.metric_key = None
         # prepare loss
         losser = _prepare_losser(loss)
         
         # sampler check
         if sampler is not None and not isinstance(sampler, Sampler):
             raise ValueError("The type of sampler should be fastNLP.BaseSampler, got {}.".format(type(sampler)))
+
+        if sampler is None:
+            sampler = RandomSampler()
+
+        if isinstance(train_data, DataSet):
+            self.data_iterator = DataSetIter(
+                dataset=train_data, batch_size=batch_size, num_workers=num_workers, sampler=sampler, drop_last=drop_last)
+        elif isinstance(train_data, BatchIter):
+            self.data_iterator = train_data
+        else:
+            raise TypeError("train_data type {} not support".format(type(train_data)))
         
-        if check_code_level > -1:
+        if check_code_level > -1 and isinstance(self.data_iterator, DataSetIter):
             _check_code(dataset=train_data, model=model, losser=losser, metrics=metrics, dev_data=dev_data,
                         metric_key=metric_key, check_level=check_code_level,
                         batch_size=min(batch_size, DEFAULT_CHECK_BATCH_SIZE))
@@ -460,8 +472,6 @@ class Trainer(object):
         self.best_dev_epoch = None
         self.best_dev_step = None
         self.best_dev_perf = None
-        self.sampler = sampler if sampler is not None else RandomSampler()
-        self.prefetch = prefetch
         self.n_steps = (len(self.train_data) // self.batch_size + int(
             len(self.train_data) % self.batch_size != 0)) * self.n_epochs
         
@@ -493,7 +503,7 @@ class Trainer(object):
         
         self.callback_manager = CallbackManager(env={"trainer": self},
                                                 callbacks=callbacks)
-    
+
     def train(self, load_best_model=True, on_exception='auto'):
         """
         使用该函数使Trainer开始训练。
@@ -572,8 +582,7 @@ class Trainer(object):
         with inner_tqdm(total=self.n_steps, postfix='loss:{0:<6.5f}', leave=False, dynamic_ncols=True) as pbar:
             self.pbar = pbar
             avg_loss = 0
-            data_iterator = Batch(self.train_data, batch_size=self.batch_size, sampler=self.sampler, as_numpy=False,
-                                  prefetch=self.prefetch)
+            data_iterator = self.data_iterator
             self.batch_per_epoch = data_iterator.num_batches
             for epoch in range(1, self.n_epochs + 1):
                 self.epoch = epoch
@@ -746,7 +755,9 @@ class Trainer(object):
 
         :return bool value: True means current results on dev set is the best.
         """
-        indicator_val = _check_eval_results(metrics, self.metric_key, self.metrics)
+        indicator, indicator_val = _check_eval_results(metrics, self.metric_key, self.metrics)
+        if self.metric_key is None:
+            self.metric_key = indicator
         is_better = True
         if self.best_metric_indicator is None:
             # first-time validation
@@ -785,15 +796,34 @@ def _get_value_info(_dict):
         strs.append(_str)
     return strs
 
-
+from numbers import Number
+from .batch import _to_tensor
 def _check_code(dataset, model, losser, metrics, batch_size=DEFAULT_CHECK_BATCH_SIZE,
                 dev_data=None, metric_key=None,
                 check_level=0):
     # check get_loss 方法
-    model_devcie = model.parameters().__next__().device
+    model_devcie = _get_model_device(model=model)
     
-    batch = Batch(dataset=dataset, batch_size=batch_size, sampler=SequentialSampler())
-    for batch_count, (batch_x, batch_y) in enumerate(batch):
+    def _iter():
+        start_idx = 0
+        while start_idx<len(dataset):
+            batch_x = {}
+            batch_y = {}
+            for field_name, field in dataset.get_all_fields().items():
+                indices = list(range(start_idx, min(start_idx+batch_size, len(dataset))))
+                if field.is_target or field.is_input:
+                    batch = field.get(indices)
+                    if field.dtype is not None and \
+                            issubclass(field.dtype, Number) and not isinstance(batch, torch.Tensor):
+                        batch, _ = _to_tensor(batch, field.dtype)
+                    if field.is_target:
+                        batch_y[field_name] = batch
+                    if field.is_input:
+                        batch_x[field_name] = batch
+            yield (batch_x, batch_y)
+            start_idx += batch_size
+
+    for batch_count, (batch_x, batch_y) in enumerate(_iter()):
         _move_dict_value_to_device(batch_x, batch_y, device=model_devcie)
         # forward check
         if batch_count == 0:
@@ -861,26 +891,16 @@ def _check_eval_results(metrics, metric_key, metric_list):
         loss, metrics = metrics
     
     if isinstance(metrics, dict):
-        if len(metrics) == 1:
-            # only single metric, just use it
-            metric_dict = list(metrics.values())[0]
-            metrics_name = list(metrics.keys())[0]
-        else:
-            metrics_name = metric_list[0].__class__.__name__
-            if metrics_name not in metrics:
-                raise RuntimeError(f"{metrics_name} is chosen to do validation, but got {metrics}")
-            metric_dict = metrics[metrics_name]
+        metric_dict = list(metrics.values())[0]  # 取第一个metric
         
-        if len(metric_dict) == 1:
+        if metric_key is None:
             indicator_val, indicator = list(metric_dict.values())[0], list(metric_dict.keys())[0]
-        elif len(metric_dict) > 1 and metric_key is None:
-            raise RuntimeError(
-                f"Got multiple metric keys: {metric_dict}, but metric_key is not set. Which one to use?")
         else:
             # metric_key is set
             if metric_key not in metric_dict:
                 raise RuntimeError(f"metric key {metric_key} not found in {metric_dict}")
             indicator_val = metric_dict[metric_key]
+            indicator = metric_key
     else:
         raise RuntimeError("Invalid metrics type. Expect {}, got {}".format((tuple, dict), type(metrics)))
-    return indicator_val
+    return indicator, indicator_val
diff --git a/fastNLP/io/base_loader.py b/fastNLP/io/base_loader.py
index adfa8ca1..465fb7e8 100644
--- a/fastNLP/io/base_loader.py
+++ b/fastNLP/io/base_loader.py
@@ -124,6 +124,14 @@ class DataInfo:
         self.embeddings = embeddings or {}
         self.datasets = datasets or {}
 
+    def __repr__(self):
+        _str = 'In total {} datasets:\n'.format(len(self.datasets))
+        for name, dataset in self.datasets.items():
+            _str += '\t{} has {} instances.\n'.format(name, len(dataset))
+        _str += 'In total {} vocabs:\n'.format(len(self.vocabs))
+        for name, vocab in self.vocabs.items():
+            _str += '\t{} has {} entries.\n'.format(name, len(vocab))
+        return _str
 
 class DataSetLoader:
     """
diff --git a/fastNLP/io/dataset_loader.py b/fastNLP/io/dataset_loader.py
index e366c6ea..a804b374 100644
--- a/fastNLP/io/dataset_loader.py
+++ b/fastNLP/io/dataset_loader.py
@@ -115,7 +115,8 @@ class ConllLoader(DataSetLoader):
     """
     别名：:class:`fastNLP.io.ConllLoader` :class:`fastNLP.io.dataset_loader.ConllLoader`
 
-    读取Conll格式的数据. 数据格式详见 http://conll.cemantix.org/2012/data.html
+    读取Conll格式的数据. 数据格式详见 http://conll.cemantix.org/2012/data.html. 数据中以"-DOCSTART-"开头的行将被忽略，因为
+        该符号在conll 2003中被用为文档分割符。
 
     列号从0开始, 每列对应内容为::
 
diff --git a/fastNLP/io/file_reader.py b/fastNLP/io/file_reader.py
index 5963bb56..34b5d7c0 100644
--- a/fastNLP/io/file_reader.py
+++ b/fastNLP/io/file_reader.py
@@ -90,11 +90,12 @@ def _read_conll(path, encoding='utf-8', indexes=None, dropna=True):
         return sample
     with open(path, 'r', encoding=encoding) as f:
         sample = []
-        start = next(f)
-        if '-DOCSTART-' not in start:
+        start = next(f).strip()
+        if '-DOCSTART-' not in start and start!='':
             sample.append(start.split())
         for line_idx, line in enumerate(f, 1):
-            if line.startswith('\n'):
+            line = line.strip()
+            if line=='':
                 if len(sample):
                     try:
                         res = parse_conll(sample)
@@ -107,7 +108,8 @@ def _read_conll(path, encoding='utf-8', indexes=None, dropna=True):
             elif line.startswith('#'):
                 continue
             else:
-                sample.append(line.split())
+                if not line.startswith('-DOCSTART-'):
+                    sample.append(line.split())
         if len(sample) > 0:
             try:
                 res = parse_conll(sample)
@@ -115,4 +117,5 @@ def _read_conll(path, encoding='utf-8', indexes=None, dropna=True):
             except Exception as e:
                 if dropna:
                     return
-                raise ValueError('invalid instance at line: {}'.format(line_idx))
+                print('invalid instance at line: {}'.format(line_idx))
+                raise e
diff --git a/fastNLP/modules/decoder/crf.py b/fastNLP/modules/decoder/crf.py
index beb2b9be..c0717d6f 100644
--- a/fastNLP/modules/decoder/crf.py
+++ b/fastNLP/modules/decoder/crf.py
@@ -9,7 +9,7 @@ from torch import nn
 from ..utils import initial_parameter
 
 
-def allowed_transitions(id2target, encoding_type='bio', include_start_end=True):
+def allowed_transitions(id2target, encoding_type='bio', include_start_end=False):
     """
     别名：:class:`fastNLP.modules.allowed_transitions`  :class:`fastNLP.modules.decoder.crf.allowed_transitions`
 
@@ -17,7 +17,7 @@ def allowed_transitions(id2target, encoding_type='bio', include_start_end=True):
 
     :param dict id2target: key是label的indices，value是str类型的tag或tag-label。value可以是只有tag的, 比如"B", "M"; 也可以是
         "B-NN", "M-NN", tag和label之间一定要用"-"隔开。一般可以通过Vocabulary.idx2word得到id2label。
-    :param str encoding_type: 支持"bio", "bmes", "bmeso"。
+    :param str encoding_type: 支持"bio", "bmes", "bmeso", "bioes"。
     :param bool include_start_end: 是否包含开始与结尾的转换。比如在bio中，b/o可以在开头，但是i不能在开头；
         为True，返回的结果中会包含(start_idx, b_idx), (start_idx, o_idx), 但是不包含(start_idx, i_idx);
         start_idx=len(id2label), end_idx=len(id2label)+1。为False, 返回的结果中不含与开始结尾相关的内容
@@ -58,7 +58,7 @@ def allowed_transitions(id2target, encoding_type='bio', include_start_end=True):
 def _is_transition_allowed(encoding_type, from_tag, from_label, to_tag, to_label):
     """
 
-    :param str encoding_type: 支持"BIO", "BMES", "BEMSO"。
+    :param str encoding_type: 支持"BIO", "BMES", "BEMSO", 'bioes'。
     :param str from_tag: 比如"B", "M"之类的标注tag. 还包括start, end等两种特殊tag
     :param str from_label: 比如"PER", "LOC"等label
     :param str to_tag: 比如"B", "M"之类的标注tag. 还包括start, end等两种特殊tag
@@ -134,9 +134,19 @@ def _is_transition_allowed(encoding_type, from_tag, from_label, to_tag, to_label
             return to_tag in ['b', 's', 'end', 'o']
         else:
             raise ValueError("Unexpect tag type {}. Expect only 'B', 'M', 'E', 'S', 'O'.".format(from_tag))
-    
+    elif encoding_type == 'bioes':
+        if from_tag == 'start':
+            return to_tag in ['b', 's', 'o']
+        elif from_tag == 'b':
+            return to_tag in ['i', 'e'] and from_label == to_label
+        elif from_tag == 'i':
+            return to_tag in ['i', 'e'] and from_label == to_label
+        elif from_tag in ['e', 's', 'o']:
+            return to_tag in ['b', 's', 'end', 'o']
+        else:
+            raise ValueError("Unexpect tag type {}. Expect only 'B', 'I', 'E', 'S', 'O'.".format(from_tag))
     else:
-        raise ValueError("Only support BIO, BMES, BMESO encoding type, got {}.".format(encoding_type))
+        raise ValueError("Only support BIO, BMES, BMESO, BIOES encoding type, got {}.".format(encoding_type))
 
 
 class ConditionalRandomField(nn.Module):
diff --git a/fastNLP/modules/encoder/__init__.py b/fastNLP/modules/encoder/__init__.py
index bdc4cbf3..431122b1 100644
--- a/fastNLP/modules/encoder/__init__.py
+++ b/fastNLP/modules/encoder/__init__.py
@@ -18,7 +18,8 @@ __all__ = [
     "VarLSTM",
     "VarGRU"
 ]
-from .bert import BertModel
+from ._bert import BertModel
+from .bert import BertWordPieceEncoder
 from .char_encoder import ConvolutionCharEncoder, LSTMCharEncoder
 from .conv_maxpool import ConvMaxpool
 from .embedding import Embedding
diff --git a/fastNLP/modules/encoder/_bert.py b/fastNLP/modules/encoder/_bert.py
index fc62ea9c..95645b74 100644
--- a/fastNLP/modules/encoder/_bert.py
+++ b/fastNLP/modules/encoder/_bert.py
@@ -6,18 +6,399 @@
 """
 
 
-import torch
-from torch import nn
 
 from ... import Vocabulary
 import collections
 
-import os
 import unicodedata
 from ...io.file_utils import _get_base_url, cached_path
-from .bert import BertModel
 import numpy as np
 from itertools import chain
+import copy
+import json
+import math
+import os
+
+import torch
+from torch import nn
+
+CONFIG_FILE = 'bert_config.json'
+MODEL_WEIGHTS = 'pytorch_model.bin'
+
+
+def gelu(x):
+    return x * 0.5 * (1.0 + torch.erf(x / math.sqrt(2.0)))
+
+
+def swish(x):
+    return x * torch.sigmoid(x)
+
+
+ACT2FN = {"gelu": gelu, "relu": torch.nn.functional.relu, "swish": swish}
+
+
+class BertLayerNorm(nn.Module):
+    def __init__(self, hidden_size, eps=1e-12):
+        super(BertLayerNorm, self).__init__()
+        self.weight = nn.Parameter(torch.ones(hidden_size))
+        self.bias = nn.Parameter(torch.zeros(hidden_size))
+        self.variance_epsilon = eps
+
+    def forward(self, x):
+        u = x.mean(-1, keepdim=True)
+        s = (x - u).pow(2).mean(-1, keepdim=True)
+        x = (x - u) / torch.sqrt(s + self.variance_epsilon)
+        return self.weight * x + self.bias
+
+
+class BertEmbeddings(nn.Module):
+    def __init__(self, vocab_size, hidden_size, max_position_embeddings, type_vocab_size, hidden_dropout_prob):
+        super(BertEmbeddings, self).__init__()
+        self.word_embeddings = nn.Embedding(vocab_size, hidden_size)
+        self.position_embeddings = nn.Embedding(max_position_embeddings, hidden_size)
+        self.token_type_embeddings = nn.Embedding(type_vocab_size, hidden_size)
+
+        # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
+        # any TensorFlow checkpoint file
+        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
+        self.dropout = nn.Dropout(hidden_dropout_prob)
+
+    def forward(self, input_ids, token_type_ids=None):
+        seq_length = input_ids.size(1)
+        position_ids = torch.arange(seq_length, dtype=torch.long, device=input_ids.device)
+        position_ids = position_ids.unsqueeze(0).expand_as(input_ids)
+        if token_type_ids is None:
+            token_type_ids = torch.zeros_like(input_ids)
+
+        words_embeddings = self.word_embeddings(input_ids)
+        position_embeddings = self.position_embeddings(position_ids)
+        token_type_embeddings = self.token_type_embeddings(token_type_ids)
+
+        embeddings = words_embeddings + position_embeddings + token_type_embeddings
+        embeddings = self.LayerNorm(embeddings)
+        embeddings = self.dropout(embeddings)
+        return embeddings
+
+
+class BertSelfAttention(nn.Module):
+    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob):
+        super(BertSelfAttention, self).__init__()
+        if hidden_size % num_attention_heads != 0:
+            raise ValueError(
+                "The hidden size (%d) is not a multiple of the number of attention "
+                "heads (%d)" % (hidden_size, num_attention_heads))
+        self.num_attention_heads = num_attention_heads
+        self.attention_head_size = int(hidden_size / num_attention_heads)
+        self.all_head_size = self.num_attention_heads * self.attention_head_size
+
+        self.query = nn.Linear(hidden_size, self.all_head_size)
+        self.key = nn.Linear(hidden_size, self.all_head_size)
+        self.value = nn.Linear(hidden_size, self.all_head_size)
+
+        self.dropout = nn.Dropout(attention_probs_dropout_prob)
+
+    def transpose_for_scores(self, x):
+        new_x_shape = x.size()[:-1] + (self.num_attention_heads, self.attention_head_size)
+        x = x.view(*new_x_shape)
+        return x.permute(0, 2, 1, 3)
+
+    def forward(self, hidden_states, attention_mask):
+        mixed_query_layer = self.query(hidden_states)
+        mixed_key_layer = self.key(hidden_states)
+        mixed_value_layer = self.value(hidden_states)
+
+        query_layer = self.transpose_for_scores(mixed_query_layer)
+        key_layer = self.transpose_for_scores(mixed_key_layer)
+        value_layer = self.transpose_for_scores(mixed_value_layer)
+
+        # Take the dot product between "query" and "key" to get the raw attention scores.
+        attention_scores = torch.matmul(query_layer, key_layer.transpose(-1, -2))
+        attention_scores = attention_scores / math.sqrt(self.attention_head_size)
+        # Apply the attention mask is (precomputed for all layers in BertModel forward() function)
+        attention_scores = attention_scores + attention_mask
+
+        # Normalize the attention scores to probabilities.
+        attention_probs = nn.Softmax(dim=-1)(attention_scores)
+
+        # This is actually dropping out entire tokens to attend to, which might
+        # seem a bit unusual, but is taken from the original Transformer paper.
+        attention_probs = self.dropout(attention_probs)
+
+        context_layer = torch.matmul(attention_probs, value_layer)
+        context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
+        new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
+        context_layer = context_layer.view(*new_context_layer_shape)
+        return context_layer
+
+
+class BertSelfOutput(nn.Module):
+    def __init__(self, hidden_size, hidden_dropout_prob):
+        super(BertSelfOutput, self).__init__()
+        self.dense = nn.Linear(hidden_size, hidden_size)
+        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
+        self.dropout = nn.Dropout(hidden_dropout_prob)
+
+    def forward(self, hidden_states, input_tensor):
+        hidden_states = self.dense(hidden_states)
+        hidden_states = self.dropout(hidden_states)
+        hidden_states = self.LayerNorm(hidden_states + input_tensor)
+        return hidden_states
+
+
+class BertAttention(nn.Module):
+    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob):
+        super(BertAttention, self).__init__()
+        self.self = BertSelfAttention(hidden_size, num_attention_heads, attention_probs_dropout_prob)
+        self.output = BertSelfOutput(hidden_size, hidden_dropout_prob)
+
+    def forward(self, input_tensor, attention_mask):
+        self_output = self.self(input_tensor, attention_mask)
+        attention_output = self.output(self_output, input_tensor)
+        return attention_output
+
+
+class BertIntermediate(nn.Module):
+    def __init__(self, hidden_size, intermediate_size, hidden_act):
+        super(BertIntermediate, self).__init__()
+        self.dense = nn.Linear(hidden_size, intermediate_size)
+        self.intermediate_act_fn = ACT2FN[hidden_act] \
+            if isinstance(hidden_act, str) else hidden_act
+
+    def forward(self, hidden_states):
+        hidden_states = self.dense(hidden_states)
+        hidden_states = self.intermediate_act_fn(hidden_states)
+        return hidden_states
+
+
+class BertOutput(nn.Module):
+    def __init__(self, hidden_size, intermediate_size, hidden_dropout_prob):
+        super(BertOutput, self).__init__()
+        self.dense = nn.Linear(intermediate_size, hidden_size)
+        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
+        self.dropout = nn.Dropout(hidden_dropout_prob)
+
+    def forward(self, hidden_states, input_tensor):
+        hidden_states = self.dense(hidden_states)
+        hidden_states = self.dropout(hidden_states)
+        hidden_states = self.LayerNorm(hidden_states + input_tensor)
+        return hidden_states
+
+
+class BertLayer(nn.Module):
+    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob,
+                 intermediate_size, hidden_act):
+        super(BertLayer, self).__init__()
+        self.attention = BertAttention(hidden_size, num_attention_heads, attention_probs_dropout_prob,
+                                       hidden_dropout_prob)
+        self.intermediate = BertIntermediate(hidden_size, intermediate_size, hidden_act)
+        self.output = BertOutput(hidden_size, intermediate_size, hidden_dropout_prob)
+
+    def forward(self, hidden_states, attention_mask):
+        attention_output = self.attention(hidden_states, attention_mask)
+        intermediate_output = self.intermediate(attention_output)
+        layer_output = self.output(intermediate_output, attention_output)
+        return layer_output
+
+
+class BertEncoder(nn.Module):
+    def __init__(self, num_hidden_layers, hidden_size, num_attention_heads, attention_probs_dropout_prob,
+                 hidden_dropout_prob,
+                 intermediate_size, hidden_act):
+        super(BertEncoder, self).__init__()
+        layer = BertLayer(hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob,
+                          intermediate_size, hidden_act)
+        self.layer = nn.ModuleList([copy.deepcopy(layer) for _ in range(num_hidden_layers)])
+
+    def forward(self, hidden_states, attention_mask, output_all_encoded_layers=True):
+        all_encoder_layers = []
+        for layer_module in self.layer:
+            hidden_states = layer_module(hidden_states, attention_mask)
+            if output_all_encoded_layers:
+                all_encoder_layers.append(hidden_states)
+        if not output_all_encoded_layers:
+            all_encoder_layers.append(hidden_states)
+        return all_encoder_layers
+
+
+class BertPooler(nn.Module):
+    def __init__(self, hidden_size):
+        super(BertPooler, self).__init__()
+        self.dense = nn.Linear(hidden_size, hidden_size)
+        self.activation = nn.Tanh()
+
+    def forward(self, hidden_states):
+        # We "pool" the model by simply taking the hidden state corresponding
+        # to the first token.
+        first_token_tensor = hidden_states[:, 0]
+        pooled_output = self.dense(first_token_tensor)
+        pooled_output = self.activation(pooled_output)
+        return pooled_output
+
+
+class BertModel(nn.Module):
+    """BERT(Bidirectional Embedding Representations from Transformers).
+
+    如果你想使用预训练好的权重矩阵，请在以下网址下载.
+    sources::
+
+    'bert-base-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-uncased.tar.gz",
+    'bert-large-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-large-uncased.tar.gz",
+    'bert-base-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-cased.tar.gz",
+    'bert-large-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-large-cased.tar.gz",
+    'bert-base-multilingual-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-multilingual-uncased.tar.gz",
+    'bert-base-multilingual-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-multilingual-cased.tar.gz",
+    'bert-base-chinese': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-chinese.tar.gz",
+
+
+    用预训练权重矩阵来建立BERT模型::
+
+        model = BertModel.from_pretrained("path/to/weights/directory")
+
+    用随机初始化权重矩阵来建立BERT模型::
+
+        model = BertModel()
+
+    :param int vocab_size: 词表大小，默认值为30522，为BERT English uncase版本的词表大小
+    :param int hidden_size: 隐层大小，默认值为768，为BERT base的版本
+    :param int num_hidden_layers: 隐藏层数，默认值为12，为BERT base的版本
+    :param int num_attention_heads: 多头注意力头数，默认值为12，为BERT base的版本
+    :param int intermediate_size: FFN隐藏层大小，默认值是3072，为BERT base的版本
+    :param str hidden_act: FFN隐藏层激活函数，默认值为``gelu``
+    :param float hidden_dropout_prob: FFN隐藏层dropout，默认值为0.1
+    :param float attention_probs_dropout_prob: Attention层的dropout，默认值为0.1
+    :param int max_position_embeddings: 最大的序列长度，默认值为512，
+    :param int type_vocab_size: 最大segment数量，默认值为2
+    :param int initializer_range: 初始化权重范围，默认值为0.02
+    """
+
+    def __init__(self, vocab_size=30522,
+                 hidden_size=768,
+                 num_hidden_layers=12,
+                 num_attention_heads=12,
+                 intermediate_size=3072,
+                 hidden_act="gelu",
+                 hidden_dropout_prob=0.1,
+                 attention_probs_dropout_prob=0.1,
+                 max_position_embeddings=512,
+                 type_vocab_size=2,
+                 initializer_range=0.02):
+        super(BertModel, self).__init__()
+        self.hidden_size = hidden_size
+        self.embeddings = BertEmbeddings(vocab_size, hidden_size, max_position_embeddings,
+                                         type_vocab_size, hidden_dropout_prob)
+        self.encoder = BertEncoder(num_hidden_layers, hidden_size, num_attention_heads,
+                                   attention_probs_dropout_prob, hidden_dropout_prob, intermediate_size,
+                                   hidden_act)
+        self.pooler = BertPooler(hidden_size)
+        self.initializer_range = initializer_range
+
+        self.apply(self.init_bert_weights)
+
+    def init_bert_weights(self, module):
+        if isinstance(module, (nn.Linear, nn.Embedding)):
+            # Slightly different from the TF version which uses truncated_normal for initialization
+            # cf https://github.com/pytorch/pytorch/pull/5617
+            module.weight.data.normal_(mean=0.0, std=self.initializer_range)
+        elif isinstance(module, BertLayerNorm):
+            module.bias.data.zero_()
+            module.weight.data.fill_(1.0)
+        if isinstance(module, nn.Linear) and module.bias is not None:
+            module.bias.data.zero_()
+
+    def forward(self, input_ids, token_type_ids=None, attention_mask=None, output_all_encoded_layers=True):
+        if attention_mask is None:
+            attention_mask = torch.ones_like(input_ids)
+        if token_type_ids is None:
+            token_type_ids = torch.zeros_like(input_ids)
+
+        # We create a 3D attention mask from a 2D tensor mask.
+        # Sizes are [batch_size, 1, 1, to_seq_length]
+        # So we can broadcast to [batch_size, num_heads, from_seq_length, to_seq_length]
+        # this attention mask is more simple than the triangular masking of causal attention
+        # used in OpenAI GPT, we just need to prepare the broadcast dimension here.
+        extended_attention_mask = attention_mask.unsqueeze(1).unsqueeze(2)
+
+        # Since attention_mask is 1.0 for positions we want to attend and 0.0 for
+        # masked positions, this operation will create a tensor which is 0.0 for
+        # positions we want to attend and -10000.0 for masked positions.
+        # Since we are adding it to the raw scores before the softmax, this is
+        # effectively the same as removing these entirely.
+        extended_attention_mask = extended_attention_mask.to(dtype=next(self.parameters()).dtype)  # fp16 compatibility
+        extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0
+
+        embedding_output = self.embeddings(input_ids, token_type_ids)
+        encoded_layers = self.encoder(embedding_output,
+                                      extended_attention_mask,
+                                      output_all_encoded_layers=output_all_encoded_layers)
+        sequence_output = encoded_layers[-1]
+        pooled_output = self.pooler(sequence_output)
+        if not output_all_encoded_layers:
+            encoded_layers = encoded_layers[-1]
+        return encoded_layers, pooled_output
+
+    @classmethod
+    def from_pretrained(cls, pretrained_model_dir, state_dict=None, *inputs, **kwargs):
+        # Load config
+        config_file = os.path.join(pretrained_model_dir, CONFIG_FILE)
+        config = json.load(open(config_file, "r"))
+        # config = BertConfig.from_json_file(config_file)
+        # logger.info("Model config {}".format(config))
+        # Instantiate model.
+        model = cls(*inputs, **config, **kwargs)
+        if state_dict is None:
+            weights_path = os.path.join(pretrained_model_dir, MODEL_WEIGHTS)
+            state_dict = torch.load(weights_path)
+
+        old_keys = []
+        new_keys = []
+        for key in state_dict.keys():
+            new_key = None
+            if 'gamma' in key:
+                new_key = key.replace('gamma', 'weight')
+            if 'beta' in key:
+                new_key = key.replace('beta', 'bias')
+            if new_key:
+                old_keys.append(key)
+                new_keys.append(new_key)
+        for old_key, new_key in zip(old_keys, new_keys):
+            state_dict[new_key] = state_dict.pop(old_key)
+
+        missing_keys = []
+        unexpected_keys = []
+        error_msgs = []
+        # copy state_dict so _load_from_state_dict can modify it
+        metadata = getattr(state_dict, '_metadata', None)
+        state_dict = state_dict.copy()
+        if metadata is not None:
+            state_dict._metadata = metadata
+
+        def load(module, prefix=''):
+            local_metadata = {} if metadata is None else metadata.get(prefix[:-1], {})
+            module._load_from_state_dict(
+                state_dict, prefix, local_metadata, True, missing_keys, unexpected_keys, error_msgs)
+            for name, child in module._modules.items():
+                if child is not None:
+                    load(child, prefix + name + '.')
+
+        load(model, prefix='' if hasattr(model, 'bert') else 'bert.')
+        if len(missing_keys) > 0:
+            print("Weights of {} not initialized from pretrained model: {}".format(
+                model.__class__.__name__, missing_keys))
+        if len(unexpected_keys) > 0:
+            print("Weights from pretrained model not used in {}: {}".format(
+                model.__class__.__name__, unexpected_keys))
+        return model
+
+
+
+
+
+
+
+
+
+
+
 
 def whitespace_tokenize(text):
     """Runs basic whitespace cleaning and splitting on a piece of text."""
@@ -547,79 +928,3 @@ class _WordPieceBertModel(nn.Module):
             outputs[l_index] = bert_outputs[l]
         return outputs
 
-class BertWordPieceEncoder(nn.Module):
-    """
-    可以通过读取vocabulary使用的Bert的Encoder。传入vocab，然后调用index_datasets方法在vocabulary中生成word piece的表示。
-
-    :param vocab: Vocabulary.
-    :param model_dir_or_name:
-    :param layers:
-    :param requires_grad:
-    """
-    def __init__(self, vocab:Vocabulary, model_dir_or_name:str='en-base', layers:str='-1',
-                 requires_grad:bool=False):
-        super().__init__()
-        PRETRAIN_URL = _get_base_url('bert')
-        # TODO 修改
-        PRETRAINED_BERT_MODEL_DIR = {'en-base': 'bert_en-80f95ea7.tar.gz',
-                                     'cn': 'elmo_cn.zip'}
-
-        if model_dir_or_name in PRETRAINED_BERT_MODEL_DIR:
-            model_name = PRETRAINED_BERT_MODEL_DIR[model_dir_or_name]
-            model_url = PRETRAIN_URL + model_name
-            model_dir = cached_path(model_url)
-            # 检查是否存在
-        elif os.path.isdir(model_dir_or_name):
-            model_dir = model_dir_or_name
-        else:
-            raise ValueError(f"Cannot recognize {model_dir_or_name}.")
-
-        self.model = _WordPieceBertModel(model_dir=model_dir, vocab=vocab, layers=layers)
-        self._embed_size = len(self.model.layers) * self.model.encoder.hidden_size
-        self.requires_grad = requires_grad
-
-    @property
-    def requires_grad(self):
-        """
-        Embedding的参数是否允许优化。True: 所有参数运行优化; False: 所有参数不允许优化; None: 部分允许优化、部分不允许
-        :return:
-        """
-        requires_grads = set([param.requires_grad for name, param in self.named_parameters()])
-        if len(requires_grads)==1:
-            return requires_grads.pop()
-        else:
-            return None
-
-    @requires_grad.setter
-    def requires_grad(self, value):
-        for name, param in self.named_parameters():
-            param.requires_grad = value
-
-    @property
-    def embed_size(self):
-        return self._embed_size
-
-    def index_datasets(self, *datasets):
-        """
-        对datasets进行word piece的index。
-
-        Example::
-
-        :param datasets:
-        :return:
-        """
-        self.model.index_dataset(*datasets)
-
-    def forward(self, words, token_type_ids=None):
-        """
-        计算words的bert embedding表示。计算之前会在每句话的开始增加[CLS]在结束增加[SEP], 并根据include_cls_sep判断要不要
-            删除这两个表示。
-
-        :param words: batch_size x max_len
-        :param token_type_ids: batch_size x max_len, 用于区分前一句和后一句话
-        :return: torch.FloatTensor. batch_size x max_len x (768*len(self.layers))
-        """
-        outputs = self.model(words, token_type_ids)
-        outputs = torch.cat([*outputs], dim=-1)
-
-        return outputs
\ No newline at end of file
diff --git a/fastNLP/modules/encoder/bert.py b/fastNLP/modules/encoder/bert.py
index 38a35fc9..e9739c28 100644
--- a/fastNLP/modules/encoder/bert.py
+++ b/fastNLP/modules/encoder/bert.py
@@ -1,378 +1,95 @@
-"""
-bert.py is modified from huggingface/pytorch-pretrained-BERT, which is licensed under the Apache License 2.0.
 
-"""
-import copy
-import json
-import math
 import os
-
-import torch
 from torch import nn
+import torch
+from ...core import Vocabulary
+from ...io.file_utils import _get_base_url, cached_path
+from ._bert import _WordPieceBertModel
 
-CONFIG_FILE = 'bert_config.json'
-MODEL_WEIGHTS = 'pytorch_model.bin'
-
-
-def gelu(x):
-    return x * 0.5 * (1.0 + torch.erf(x / math.sqrt(2.0)))
-
-
-def swish(x):
-    return x * torch.sigmoid(x)
-
-
-ACT2FN = {"gelu": gelu, "relu": torch.nn.functional.relu, "swish": swish}
-
-
-class BertLayerNorm(nn.Module):
-    def __init__(self, hidden_size, eps=1e-12):
-        super(BertLayerNorm, self).__init__()
-        self.weight = nn.Parameter(torch.ones(hidden_size))
-        self.bias = nn.Parameter(torch.zeros(hidden_size))
-        self.variance_epsilon = eps
-
-    def forward(self, x):
-        u = x.mean(-1, keepdim=True)
-        s = (x - u).pow(2).mean(-1, keepdim=True)
-        x = (x - u) / torch.sqrt(s + self.variance_epsilon)
-        return self.weight * x + self.bias
-
-
-class BertEmbeddings(nn.Module):
-    def __init__(self, vocab_size, hidden_size, max_position_embeddings, type_vocab_size, hidden_dropout_prob):
-        super(BertEmbeddings, self).__init__()
-        self.word_embeddings = nn.Embedding(vocab_size, hidden_size)
-        self.position_embeddings = nn.Embedding(max_position_embeddings, hidden_size)
-        self.token_type_embeddings = nn.Embedding(type_vocab_size, hidden_size)
-
-        # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
-        # any TensorFlow checkpoint file
-        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
-        self.dropout = nn.Dropout(hidden_dropout_prob)
-
-    def forward(self, input_ids, token_type_ids=None):
-        seq_length = input_ids.size(1)
-        position_ids = torch.arange(seq_length, dtype=torch.long, device=input_ids.device)
-        position_ids = position_ids.unsqueeze(0).expand_as(input_ids)
-        if token_type_ids is None:
-            token_type_ids = torch.zeros_like(input_ids)
-
-        words_embeddings = self.word_embeddings(input_ids)
-        position_embeddings = self.position_embeddings(position_ids)
-        token_type_embeddings = self.token_type_embeddings(token_type_ids)
-
-        embeddings = words_embeddings + position_embeddings + token_type_embeddings
-        embeddings = self.LayerNorm(embeddings)
-        embeddings = self.dropout(embeddings)
-        return embeddings
-
-
-class BertSelfAttention(nn.Module):
-    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob):
-        super(BertSelfAttention, self).__init__()
-        if hidden_size % num_attention_heads != 0:
-            raise ValueError(
-                "The hidden size (%d) is not a multiple of the number of attention "
-                "heads (%d)" % (hidden_size, num_attention_heads))
-        self.num_attention_heads = num_attention_heads
-        self.attention_head_size = int(hidden_size / num_attention_heads)
-        self.all_head_size = self.num_attention_heads * self.attention_head_size
-
-        self.query = nn.Linear(hidden_size, self.all_head_size)
-        self.key = nn.Linear(hidden_size, self.all_head_size)
-        self.value = nn.Linear(hidden_size, self.all_head_size)
-
-        self.dropout = nn.Dropout(attention_probs_dropout_prob)
-
-    def transpose_for_scores(self, x):
-        new_x_shape = x.size()[:-1] + (self.num_attention_heads, self.attention_head_size)
-        x = x.view(*new_x_shape)
-        return x.permute(0, 2, 1, 3)
-
-    def forward(self, hidden_states, attention_mask):
-        mixed_query_layer = self.query(hidden_states)
-        mixed_key_layer = self.key(hidden_states)
-        mixed_value_layer = self.value(hidden_states)
-
-        query_layer = self.transpose_for_scores(mixed_query_layer)
-        key_layer = self.transpose_for_scores(mixed_key_layer)
-        value_layer = self.transpose_for_scores(mixed_value_layer)
-
-        # Take the dot product between "query" and "key" to get the raw attention scores.
-        attention_scores = torch.matmul(query_layer, key_layer.transpose(-1, -2))
-        attention_scores = attention_scores / math.sqrt(self.attention_head_size)
-        # Apply the attention mask is (precomputed for all layers in BertModel forward() function)
-        attention_scores = attention_scores + attention_mask
-
-        # Normalize the attention scores to probabilities.
-        attention_probs = nn.Softmax(dim=-1)(attention_scores)
-
-        # This is actually dropping out entire tokens to attend to, which might
-        # seem a bit unusual, but is taken from the original Transformer paper.
-        attention_probs = self.dropout(attention_probs)
-
-        context_layer = torch.matmul(attention_probs, value_layer)
-        context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
-        new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
-        context_layer = context_layer.view(*new_context_layer_shape)
-        return context_layer
-
-
-class BertSelfOutput(nn.Module):
-    def __init__(self, hidden_size, hidden_dropout_prob):
-        super(BertSelfOutput, self).__init__()
-        self.dense = nn.Linear(hidden_size, hidden_size)
-        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
-        self.dropout = nn.Dropout(hidden_dropout_prob)
-
-    def forward(self, hidden_states, input_tensor):
-        hidden_states = self.dense(hidden_states)
-        hidden_states = self.dropout(hidden_states)
-        hidden_states = self.LayerNorm(hidden_states + input_tensor)
-        return hidden_states
-
-
-class BertAttention(nn.Module):
-    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob):
-        super(BertAttention, self).__init__()
-        self.self = BertSelfAttention(hidden_size, num_attention_heads, attention_probs_dropout_prob)
-        self.output = BertSelfOutput(hidden_size, hidden_dropout_prob)
-
-    def forward(self, input_tensor, attention_mask):
-        self_output = self.self(input_tensor, attention_mask)
-        attention_output = self.output(self_output, input_tensor)
-        return attention_output
-
-
-class BertIntermediate(nn.Module):
-    def __init__(self, hidden_size, intermediate_size, hidden_act):
-        super(BertIntermediate, self).__init__()
-        self.dense = nn.Linear(hidden_size, intermediate_size)
-        self.intermediate_act_fn = ACT2FN[hidden_act] \
-            if isinstance(hidden_act, str) else hidden_act
-
-    def forward(self, hidden_states):
-        hidden_states = self.dense(hidden_states)
-        hidden_states = self.intermediate_act_fn(hidden_states)
-        return hidden_states
-
-
-class BertOutput(nn.Module):
-    def __init__(self, hidden_size, intermediate_size, hidden_dropout_prob):
-        super(BertOutput, self).__init__()
-        self.dense = nn.Linear(intermediate_size, hidden_size)
-        self.LayerNorm = BertLayerNorm(hidden_size, eps=1e-12)
-        self.dropout = nn.Dropout(hidden_dropout_prob)
-
-    def forward(self, hidden_states, input_tensor):
-        hidden_states = self.dense(hidden_states)
-        hidden_states = self.dropout(hidden_states)
-        hidden_states = self.LayerNorm(hidden_states + input_tensor)
-        return hidden_states
-
-
-class BertLayer(nn.Module):
-    def __init__(self, hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob,
-                 intermediate_size, hidden_act):
-        super(BertLayer, self).__init__()
-        self.attention = BertAttention(hidden_size, num_attention_heads, attention_probs_dropout_prob,
-                                       hidden_dropout_prob)
-        self.intermediate = BertIntermediate(hidden_size, intermediate_size, hidden_act)
-        self.output = BertOutput(hidden_size, intermediate_size, hidden_dropout_prob)
-
-    def forward(self, hidden_states, attention_mask):
-        attention_output = self.attention(hidden_states, attention_mask)
-        intermediate_output = self.intermediate(attention_output)
-        layer_output = self.output(intermediate_output, attention_output)
-        return layer_output
-
-
-class BertEncoder(nn.Module):
-    def __init__(self, num_hidden_layers, hidden_size, num_attention_heads, attention_probs_dropout_prob,
-                 hidden_dropout_prob,
-                 intermediate_size, hidden_act):
-        super(BertEncoder, self).__init__()
-        layer = BertLayer(hidden_size, num_attention_heads, attention_probs_dropout_prob, hidden_dropout_prob,
-                          intermediate_size, hidden_act)
-        self.layer = nn.ModuleList([copy.deepcopy(layer) for _ in range(num_hidden_layers)])
-
-    def forward(self, hidden_states, attention_mask, output_all_encoded_layers=True):
-        all_encoder_layers = []
-        for layer_module in self.layer:
-            hidden_states = layer_module(hidden_states, attention_mask)
-            if output_all_encoded_layers:
-                all_encoder_layers.append(hidden_states)
-        if not output_all_encoded_layers:
-            all_encoder_layers.append(hidden_states)
-        return all_encoder_layers
-
-
-class BertPooler(nn.Module):
-    def __init__(self, hidden_size):
-        super(BertPooler, self).__init__()
-        self.dense = nn.Linear(hidden_size, hidden_size)
-        self.activation = nn.Tanh()
-
-    def forward(self, hidden_states):
-        # We "pool" the model by simply taking the hidden state corresponding
-        # to the first token.
-        first_token_tensor = hidden_states[:, 0]
-        pooled_output = self.dense(first_token_tensor)
-        pooled_output = self.activation(pooled_output)
-        return pooled_output
-
-
-class BertModel(nn.Module):
-    """BERT(Bidirectional Embedding Representations from Transformers).
-
-    如果你想使用预训练好的权重矩阵，请在以下网址下载.
-    sources::
-
-    'bert-base-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-uncased.tar.gz",
-    'bert-large-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-large-uncased.tar.gz",
-    'bert-base-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-cased.tar.gz",
-    'bert-large-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-large-cased.tar.gz",
-    'bert-base-multilingual-uncased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-multilingual-uncased.tar.gz",
-    'bert-base-multilingual-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-multilingual-cased.tar.gz",
-    'bert-base-chinese': "https://s3.amazonaws.com/models.huggingface.co/bert/bert-base-chinese.tar.gz",
-
-
-    用预训练权重矩阵来建立BERT模型::
-
-        model = BertModel.from_pretrained("path/to/weights/directory")
-
-    用随机初始化权重矩阵来建立BERT模型::
-
-        model = BertModel()
 
-    :param int vocab_size: 词表大小，默认值为30522，为BERT English uncase版本的词表大小
-    :param int hidden_size: 隐层大小，默认值为768，为BERT base的版本
-    :param int num_hidden_layers: 隐藏层数，默认值为12，为BERT base的版本
-    :param int num_attention_heads: 多头注意力头数，默认值为12，为BERT base的版本
-    :param int intermediate_size: FFN隐藏层大小，默认值是3072，为BERT base的版本
-    :param str hidden_act: FFN隐藏层激活函数，默认值为``gelu``
-    :param float hidden_dropout_prob: FFN隐藏层dropout，默认值为0.1
-    :param float attention_probs_dropout_prob: Attention层的dropout，默认值为0.1
-    :param int max_position_embeddings: 最大的序列长度，默认值为512，
-    :param int type_vocab_size: 最大segment数量，默认值为2
-    :param int initializer_range: 初始化权重范围，默认值为0.02
+class BertWordPieceEncoder(nn.Module):
     """
+    可以通过读取vocabulary使用的Bert的Encoder。传入vocab，然后调用index_datasets方法在vocabulary中生成word piece的表示。
 
-    def __init__(self, vocab_size=30522,
-                 hidden_size=768,
-                 num_hidden_layers=12,
-                 num_attention_heads=12,
-                 intermediate_size=3072,
-                 hidden_act="gelu",
-                 hidden_dropout_prob=0.1,
-                 attention_probs_dropout_prob=0.1,
-                 max_position_embeddings=512,
-                 type_vocab_size=2,
-                 initializer_range=0.02):
-        super(BertModel, self).__init__()
-        self.hidden_size = hidden_size
-        self.embeddings = BertEmbeddings(vocab_size, hidden_size, max_position_embeddings,
-                                         type_vocab_size, hidden_dropout_prob)
-        self.encoder = BertEncoder(num_hidden_layers, hidden_size, num_attention_heads,
-                                   attention_probs_dropout_prob, hidden_dropout_prob, intermediate_size,
-                                   hidden_act)
-        self.pooler = BertPooler(hidden_size)
-        self.initializer_range = initializer_range
-
-        self.apply(self.init_bert_weights)
-
-    def init_bert_weights(self, module):
-        if isinstance(module, (nn.Linear, nn.Embedding)):
-            # Slightly different from the TF version which uses truncated_normal for initialization
-            # cf https://github.com/pytorch/pytorch/pull/5617
-            module.weight.data.normal_(mean=0.0, std=self.initializer_range)
-        elif isinstance(module, BertLayerNorm):
-            module.bias.data.zero_()
-            module.weight.data.fill_(1.0)
-        if isinstance(module, nn.Linear) and module.bias is not None:
-            module.bias.data.zero_()
-
-    def forward(self, input_ids, token_type_ids=None, attention_mask=None, output_all_encoded_layers=True):
-        if attention_mask is None:
-            attention_mask = torch.ones_like(input_ids)
-        if token_type_ids is None:
-            token_type_ids = torch.zeros_like(input_ids)
-
-        # We create a 3D attention mask from a 2D tensor mask.
-        # Sizes are [batch_size, 1, 1, to_seq_length]
-        # So we can broadcast to [batch_size, num_heads, from_seq_length, to_seq_length]
-        # this attention mask is more simple than the triangular masking of causal attention
-        # used in OpenAI GPT, we just need to prepare the broadcast dimension here.
-        extended_attention_mask = attention_mask.unsqueeze(1).unsqueeze(2)
-
-        # Since attention_mask is 1.0 for positions we want to attend and 0.0 for
-        # masked positions, this operation will create a tensor which is 0.0 for
-        # positions we want to attend and -10000.0 for masked positions.
-        # Since we are adding it to the raw scores before the softmax, this is
-        # effectively the same as removing these entirely.
-        extended_attention_mask = extended_attention_mask.to(dtype=next(self.parameters()).dtype)  # fp16 compatibility
-        extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0
-
-        embedding_output = self.embeddings(input_ids, token_type_ids)
-        encoded_layers = self.encoder(embedding_output,
-                                      extended_attention_mask,
-                                      output_all_encoded_layers=output_all_encoded_layers)
-        sequence_output = encoded_layers[-1]
-        pooled_output = self.pooler(sequence_output)
-        if not output_all_encoded_layers:
-            encoded_layers = encoded_layers[-1]
-        return encoded_layers, pooled_output
-
-    @classmethod
-    def from_pretrained(cls, pretrained_model_dir, state_dict=None, *inputs, **kwargs):
-        # Load config
-        config_file = os.path.join(pretrained_model_dir, CONFIG_FILE)
-        config = json.load(open(config_file, "r"))
-        # config = BertConfig.from_json_file(config_file)
-        # logger.info("Model config {}".format(config))
-        # Instantiate model.
-        model = cls(*inputs, **config, **kwargs)
-        if state_dict is None:
-            weights_path = os.path.join(pretrained_model_dir, MODEL_WEIGHTS)
-            state_dict = torch.load(weights_path)
-
-        old_keys = []
-        new_keys = []
-        for key in state_dict.keys():
-            new_key = None
-            if 'gamma' in key:
-                new_key = key.replace('gamma', 'weight')
-            if 'beta' in key:
-                new_key = key.replace('beta', 'bias')
-            if new_key:
-                old_keys.append(key)
-                new_keys.append(new_key)
-        for old_key, new_key in zip(old_keys, new_keys):
-            state_dict[new_key] = state_dict.pop(old_key)
-
-        missing_keys = []
-        unexpected_keys = []
-        error_msgs = []
-        # copy state_dict so _load_from_state_dict can modify it
-        metadata = getattr(state_dict, '_metadata', None)
-        state_dict = state_dict.copy()
-        if metadata is not None:
-            state_dict._metadata = metadata
-
-        def load(module, prefix=''):
-            local_metadata = {} if metadata is None else metadata.get(prefix[:-1], {})
-            module._load_from_state_dict(
-                state_dict, prefix, local_metadata, True, missing_keys, unexpected_keys, error_msgs)
-            for name, child in module._modules.items():
-                if child is not None:
-                    load(child, prefix + name + '.')
-
-        load(model, prefix='' if hasattr(model, 'bert') else 'bert.')
-        if len(missing_keys) > 0:
-            print("Weights of {} not initialized from pretrained model: {}".format(
-                model.__class__.__name__, missing_keys))
-        if len(unexpected_keys) > 0:
-            print("Weights from pretrained model not used in {}: {}".format(
-                model.__class__.__name__, unexpected_keys))
-        return model
+    :param fastNLP.Vocabulary vocab: 词表
+    :param str model_dir_or_name: 模型所在目录或者模型的名称。默认值为``en-base-uncased``
+    :param str layers:最终结果中的表示。以','隔开层数，可以以负数去索引倒数几层
+    :param bool requires_grad: 是否需要gradient。
+    """
+    def __init__(self, vocab:Vocabulary, model_dir_or_name:str='en-base', layers:str='-1',
+                 requires_grad:bool=False):
+        super().__init__()
+        PRETRAIN_URL = _get_base_url('bert')
+        PRETRAINED_BERT_MODEL_DIR = {'en': 'bert-base-cased-f89bfe08.zip',
+                                     'en-base-uncased': 'bert-base-uncased-3413b23c.zip',
+                                     'en-base-cased': 'bert-base-cased-f89bfe08.zip',
+                                     'en-large-uncased': 'bert-large-uncased-20939f45.zip',
+                                     'en-large-cased': 'bert-large-cased-e0cf90fc.zip',
+
+                                     'cn': 'bert-base-chinese-29d0a84a.zip',
+                                     'cn-base': 'bert-base-chinese-29d0a84a.zip',
+
+                                     'multilingual': 'bert-base-multilingual-cased-1bd364ee.zip',
+                                     'multilingual-base-uncased': 'bert-base-multilingual-uncased-f8730fe4.zip',
+                                     'multilingual-base-cased': 'bert-base-multilingual-cased-1bd364ee.zip',
+                                     }
+
+        if model_dir_or_name in PRETRAINED_BERT_MODEL_DIR:
+            model_name = PRETRAINED_BERT_MODEL_DIR[model_dir_or_name]
+            model_url = PRETRAIN_URL + model_name
+            model_dir = cached_path(model_url)
+            # 检查是否存在
+        elif os.path.isdir(model_dir_or_name):
+            model_dir = model_dir_or_name
+        else:
+            raise ValueError(f"Cannot recognize {model_dir_or_name}.")
+
+        self.model = _WordPieceBertModel(model_dir=model_dir, vocab=vocab, layers=layers)
+        self._embed_size = len(self.model.layers) * self.model.encoder.hidden_size
+        self.requires_grad = requires_grad
+
+    @property
+    def requires_grad(self):
+        """
+        Embedding的参数是否允许优化。True: 所有参数运行优化; False: 所有参数不允许优化; None: 部分允许优化、部分不允许
+        :return:
+        """
+        requires_grads = set([param.requires_grad for name, param in self.named_parameters()])
+        if len(requires_grads)==1:
+            return requires_grads.pop()
+        else:
+            return None
+
+    @requires_grad.setter
+    def requires_grad(self, value):
+        for name, param in self.named_parameters():
+            param.requires_grad = value
+
+    @property
+    def embed_size(self):
+        return self._embed_size
+
+    def index_datasets(self, *datasets):
+        """
+        根据datasets中的'words'列对datasets进行word piece的index。
+
+        Example::
+
+        :param datasets:
+        :return:
+        """
+        self.model.index_dataset(*datasets)
+
+    def forward(self, words, token_type_ids=None):
+        """
+        计算words的bert embedding表示。计算之前会在每句话的开始增加[CLS]在结束增加[SEP], 并根据include_cls_sep判断要不要
+            删除这两个表示。
+
+        :param words: batch_size x max_len
+        :param token_type_ids: batch_size x max_len, 用于区分前一句和后一句话
+        :return: torch.FloatTensor. batch_size x max_len x (768*len(self.layers))
+        """
+        outputs = self.model(words, token_type_ids)
+        outputs = torch.cat([*outputs], dim=-1)
+
+        return outputs
\ No newline at end of file
diff --git a/fastNLP/modules/encoder/embedding.py b/fastNLP/modules/encoder/embedding.py
index 5f0b6c3b..e8fe903b 100644
--- a/fastNLP/modules/encoder/embedding.py
+++ b/fastNLP/modules/encoder/embedding.py
@@ -15,7 +15,7 @@ from ...io.file_utils import cached_path, _get_base_url
 from ._bert import _WordBertModel
 from typing import List
 
-from ... import DataSet, Batch, SequentialSampler
+from ... import DataSet, DataSetIter, SequentialSampler
 from ...core.utils import _move_model_to_device, _get_model_device
 
 
@@ -157,7 +157,6 @@ class StaticEmbedding(TokenEmbedding):
         super(StaticEmbedding, self).__init__(vocab)
 
         # 优先定义需要下载的static embedding有哪些。这里估计需要自己搞一个server，
-        PRETRAIN_URL = _get_base_url('static')
         PRETRAIN_STATIC_FILES = {
             'en': 'glove.840B.300d-cc1ad5e1.tar.gz',
             'en-glove-840b-300': 'glove.840B.300d-cc1ad5e1.tar.gz',
@@ -170,6 +169,7 @@ class StaticEmbedding(TokenEmbedding):
 
         # 得到cache_path
         if model_dir_or_name.lower() in PRETRAIN_STATIC_FILES:
+            PRETRAIN_URL = _get_base_url('static')
             model_name = PRETRAIN_STATIC_FILES[model_dir_or_name]
             model_url = PRETRAIN_URL + model_name
             model_path = cached_path(model_url)
@@ -234,7 +234,7 @@ class ContextualEmbedding(TokenEmbedding):
         with torch.no_grad():
             for index, dataset in enumerate(datasets):
                 try:
-                    batch = Batch(dataset, batch_size=batch_size, sampler=SequentialSampler(), prefetch=False)
+                    batch = DataSetIter(dataset, batch_size=batch_size, sampler=SequentialSampler())
                     for batch_x, batch_y in batch:
                         words = batch_x['words'].to(device)
                         words_list = words.tolist()
@@ -325,11 +325,11 @@ class ElmoEmbedding(ContextualEmbedding):
         self.layers = layers
 
         # 根据model_dir_or_name检查是否存在并下载
-        PRETRAIN_URL = _get_base_url('elmo')
         PRETRAINED_ELMO_MODEL_DIR = {'en': 'elmo_en-d39843fe.tar.gz',
                                      'cn': 'elmo_cn-5e9b34e2.tar.gz'}
 
         if model_dir_or_name.lower() in PRETRAINED_ELMO_MODEL_DIR:
+            PRETRAIN_URL = _get_base_url('elmo')
             model_name = PRETRAINED_ELMO_MODEL_DIR[model_dir_or_name]
             model_url = PRETRAIN_URL + model_name
             model_dir = cached_path(model_url)
@@ -383,7 +383,7 @@ class ElmoEmbedding(ContextualEmbedding):
     def requires_grad(self, value):
         for name, param in self.named_parameters():
             if 'words_to_chars_embedding' in name: # 这个不能加入到requires_grad中
-                pass
+                continue
             param.requires_grad = value
 
 
@@ -411,7 +411,6 @@ class BertEmbedding(ContextualEmbedding):
                  pool_method: str='first', include_cls_sep: bool=False, requires_grad: bool=False):
         super(BertEmbedding, self).__init__(vocab)
         # 根据model_dir_or_name检查是否存在并下载
-        PRETRAIN_URL = _get_base_url('bert')
         PRETRAINED_BERT_MODEL_DIR = {'en': 'bert-base-cased-f89bfe08.zip',
                                      'en-base-uncased': 'bert-base-uncased-3413b23c.zip',
                                      'en-base-cased': 'bert-base-cased-f89bfe08.zip',
@@ -427,6 +426,7 @@ class BertEmbedding(ContextualEmbedding):
                                      }
 
         if model_dir_or_name.lower() in PRETRAINED_BERT_MODEL_DIR:
+            PRETRAIN_URL = _get_base_url('bert')
             model_name = PRETRAINED_BERT_MODEL_DIR[model_dir_or_name]
             model_url = PRETRAIN_URL + model_name
             model_dir = cached_path(model_url)
@@ -478,7 +478,7 @@ class BertEmbedding(ContextualEmbedding):
     def requires_grad(self, value):
         for name, param in self.named_parameters():
             if 'word_pieces_lengths' in name:  # 这个不能加入到requires_grad中
-                pass
+                continue
             param.requires_grad = value
 
 
@@ -566,6 +566,7 @@ class CNNCharEmbedding(TokenEmbedding):
             for i in range(len(kernel_sizes))])
         self._embed_size = embed_size
         self.fc = nn.Linear(sum(filter_nums), embed_size)
+        self.init_param()
 
     def forward(self, words):
         """
@@ -618,9 +619,17 @@ class CNNCharEmbedding(TokenEmbedding):
     def requires_grad(self, value):
         for name, param in self.named_parameters():
             if 'words_to_chars_embedding' in name or 'word_lengths' in name:  # 这个不能加入到requires_grad中
-                pass
+                continue
             param.requires_grad = value
 
+    def init_param(self):
+        for name, param in self.named_parameters():
+            if 'words_to_chars_embedding' in name or 'word_lengths' in name:  # 这个不能reset
+                continue
+            if param.data.dim()>1:
+                nn.init.xavier_normal_(param, 1)
+            else:
+                nn.init.uniform_(param, -1, 1)
 
 class LSTMCharEmbedding(TokenEmbedding):
     """
@@ -744,7 +753,7 @@ class LSTMCharEmbedding(TokenEmbedding):
     def requires_grad(self, value):
         for name, param in self.named_parameters():
             if 'words_to_chars_embedding' in name or 'word_lengths' in name:  # 这个不能加入到requires_grad中
-                pass
+                continue
             param.requires_grad = value
 
 
diff --git a/fastNLP/modules/encoder/lstm.py b/fastNLP/modules/encoder/lstm.py
index b4d3aff2..3b97f4a7 100644
--- a/fastNLP/modules/encoder/lstm.py
+++ b/fastNLP/modules/encoder/lstm.py
@@ -35,8 +35,18 @@ class LSTM(nn.Module):
         self.batch_first = batch_first
         self.lstm = nn.LSTM(input_size, hidden_size, num_layers, bias=bias, batch_first=batch_first,
                             dropout=dropout, bidirectional=bidirectional)
+        self.init_param()
         initial_parameter(self, initial_method)
-    
+
+    def init_param(self):
+        for name, param in self.named_parameters():
+            if 'bias_i' in name:
+                param.data.fill_(1)
+            elif 'bias_h' in name:
+                param.data.fill_(0)
+            else:
+                nn.init.xavier_normal_(param)
+
     def forward(self, x, seq_len=None, h0=None, c0=None):
         """
 
diff --git a/reproduction/Biaffine_parser/run.py b/reproduction/Biaffine_parser/run.py
index a69d3d58..13c79b83 100644
--- a/reproduction/Biaffine_parser/run.py
+++ b/reproduction/Biaffine_parser/run.py
@@ -184,11 +184,8 @@ def train(path):
                         m.weight.requires_grad = True
 
     # Trainer
-    trainer = Trainer(model=model, train_data=train_data, dev_data=dev_data,
-                      loss=ParserLoss(), metrics=ParserMetric(), metric_key='UAS',
-                      **train_args.data,
-                      optimizer=fastNLP.Adam(**optim_args.data),
-                      save_path=path,
+    trainer = Trainer(train_data=train_data, model=model, optimizer=fastNLP.Adam(**optim_args.data), loss=ParserLoss(),
+                      dev_data=dev_data, metrics=ParserMetric(), metric_key='UAS', save_path=path,
                       callbacks=[MyCallback()])
 
     # Start training
diff --git a/reproduction/POS_tagging/train_pos_tag.py b/reproduction/POS_tagging/train_pos_tag.py
index ccf7aa1e..a71531a4 100644
--- a/reproduction/POS_tagging/train_pos_tag.py
+++ b/reproduction/POS_tagging/train_pos_tag.py
@@ -89,11 +89,11 @@ def train(train_data_path, dev_data_path, checkpoint=None, save=None):
         model = torch.load(checkpoint)
 
     # call trainer to train
-    trainer = Trainer(dataset, model, loss=None, metrics=SpanFPreRecMetric(tag_proc.vocab, pred="predict",
-                                                                           target="truth",
-                                                                           seq_lens="word_seq_origin_len"),
-                      dev_data=dev_data, metric_key="f",
-                      use_tqdm=True, use_cuda=True, print_every=10, n_epochs=20, save_path=save)
+    trainer = Trainer(dataset, model, loss=None, n_epochs=20, print_every=10, dev_data=dev_data,
+                      metrics=SpanFPreRecMetric(tag_proc.vocab, pred="predict",
+                                                target="truth",
+                                                seq_lens="word_seq_origin_len"), metric_key="f", save_path=save,
+                      use_tqdm=True)
     trainer.train(load_best_model=True)
 
     # save model & pipeline
diff --git a/reproduction/Star_transformer/train.py b/reproduction/Star_transformer/train.py
index dee85c38..6fb58daf 100644
--- a/reproduction/Star_transformer/train.py
+++ b/reproduction/Star_transformer/train.py
@@ -149,14 +149,10 @@ def train():
     ) if x.requires_grad and x.size(0) != len(word_v)]
     optim_cfg = [{'params': model.enc.embedding.parameters(), 'lr': g_args.lr*0.1},
                  {'params': ex_param, 'lr': g_args.lr, 'weight_decay': g_args.w_decay}, ]
-    trainer = FN.Trainer(model=model, train_data=train_data, dev_data=dev_data,
-                         loss=loss, metrics=metric, metric_key=metric_key,
-                         optimizer=torch.optim.Adam(optim_cfg),
-                         n_epochs=g_args.ep, batch_size=g_args.bsz, print_every=10, validate_every=3000,
-                         device=device,
-                         use_tqdm=False, prefetch=False,
-                         save_path=g_args.log,
-                         callbacks=[MyCallback()])
+    trainer = FN.Trainer(train_data=train_data, model=model, optimizer=torch.optim.Adam(optim_cfg), loss=loss,
+                         batch_size=g_args.bsz, n_epochs=g_args.ep, print_every=10, dev_data=dev_data, metrics=metric,
+                         metric_key=metric_key, validate_every=3000, save_path=g_args.log, use_tqdm=False,
+                         device=device, callbacks=[MyCallback()])
 
     trainer.train()
     tester = FN.Tester(data=test_data, model=model, metrics=metric,
diff --git a/reproduction/matching/snli.py b/reproduction/matching/snli.py
index b389aa11..d7f392bd 100644
--- a/reproduction/matching/snli.py
+++ b/reproduction/matching/snli.py
@@ -70,19 +70,10 @@ test_data = preprocess_data(test_data, bert_dirs)
 
 model = BertForNLI(bert_dir=bert_dirs)
 
-trainer = Trainer(
-    train_data=train_data,
-    model=model,
-    optimizer=Adam(lr=2e-5, model_params=model.parameters()),
-    batch_size=torch.cuda.device_count() * 12,
-    n_epochs=4,
-    print_every=-1,
-    dev_data=dev_data,
-    metrics=AccuracyMetric(),
-    metric_key='acc',
-    device=[i for i in range(torch.cuda.device_count())],
-    check_code_level=-1
-)
+trainer = Trainer(train_data=train_data, model=model, optimizer=Adam(lr=2e-5, model_params=model.parameters()),
+                  batch_size=torch.cuda.device_count() * 12, n_epochs=4, print_every=-1, dev_data=dev_data,
+                  metrics=AccuracyMetric(), metric_key='acc', device=[i for i in range(torch.cuda.device_count())],
+                  check_code_level=-1)
 trainer.train(load_best_model=True)
 
 tester = Tester(
diff --git a/reproduction/utils.py b/reproduction/utils.py
index 0d06c99c..26b2014c 100644
--- a/reproduction/utils.py
+++ b/reproduction/utils.py
@@ -13,7 +13,8 @@ def check_dataloader_paths(paths:Union[str, Dict[str, str]])->Dict[str, str]:
     }
     如果paths为不合法的，将直接进行raise相应的错误
 
-    :param paths: 路径
+    :param paths: 路径. 可以为一个文件路径(则认为该文件就是train的文件); 可以为一个文件目录，将在该目录下寻找train.txt,
+        test.txt, dev.txt; 可以为一个dict, 则key是用户自定义的某个文件的名称，value是这个文件的路径。
     :return:
     """
     if isinstance(paths, str):
diff --git a/test/core/test_batch.py b/test/core/test_batch.py
index d1f93b9c..aa9808ee 100644
--- a/test/core/test_batch.py
+++ b/test/core/test_batch.py
@@ -3,7 +3,7 @@ import unittest
 import numpy as np
 import torch
 
-from fastNLP import Batch
+from fastNLP import DataSetIter
 from fastNLP import DataSet
 from fastNLP import Instance
 from fastNLP import SequentialSampler
@@ -57,7 +57,7 @@ class TestCase1(unittest.TestCase):
         dataset = construct_dataset(
             [["FastNLP", "is", "the", "most", "beautiful", "tool", "in", "the", "world"] for _ in range(40)])
         dataset.set_target()
-        batch = Batch(dataset, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
+        batch = DataSetIter(dataset, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
         
         cnt = 0
         for _, _ in batch:
@@ -68,7 +68,7 @@ class TestCase1(unittest.TestCase):
         ds = DataSet({"x": [[1, 2, 3, 4]] * 40, "y": [[5, 6]] * 40})
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
         for x, y in iter:
             self.assertTrue(isinstance(x["x"], np.ndarray) and isinstance(y["y"], np.ndarray))
             self.assertEqual(len(x["x"]), 4)
@@ -81,7 +81,7 @@ class TestCase1(unittest.TestCase):
                       "y": [[4, 3, 2, 1], [3, 2, 1], [2, 1], [1]] * 10})
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
         for x, y in iter:
             self.assertEqual(x["x"].shape, (4, 4))
             self.assertEqual(y["y"].shape, (4, 4))
@@ -91,7 +91,7 @@ class TestCase1(unittest.TestCase):
                       "y": np.array([[4, 3, 2, 1], [3, 2, 1], [2, 1], [1]] * 10)})
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=True)
         for x, y in iter:
             self.assertEqual(x["x"].shape, (4, 4))
             self.assertEqual(y["y"].shape, (4, 4))
@@ -101,7 +101,7 @@ class TestCase1(unittest.TestCase):
                       "y": [[4, 3, 2, 1], [3, 2, 1], [2, 1], [1]] * 10})
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
         for x, y in iter:
             self.assertTrue(isinstance(x["x"], torch.Tensor))
             self.assertEqual(tuple(x["x"].shape), (4, 4))
@@ -113,7 +113,7 @@ class TestCase1(unittest.TestCase):
                       "y": np.array([[4, 3, 2, 1], [3, 2, 1], [2, 1], [1]] * 10)})
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
         for x, y in iter:
             self.assertTrue(isinstance(x["x"], torch.Tensor))
             self.assertEqual(tuple(x["x"].shape), (4, 4))
@@ -125,7 +125,7 @@ class TestCase1(unittest.TestCase):
                      [Instance(x=[1, 2, 3, 4], y=[3, 4, 5, 6]) for _ in range(2)])
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
         for x, y in iter:
             self.assertTrue(isinstance(x["x"], torch.Tensor))
             self.assertEqual(tuple(x["x"].shape), (4, 4))
@@ -137,7 +137,7 @@ class TestCase1(unittest.TestCase):
                      [Instance(x=np.array([1, 2, 3, 4]), y=np.array([3, 4, 5, 6])) for _ in range(2)])
         ds.set_input("x")
         ds.set_target("y")
-        iter = Batch(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
+        iter = DataSetIter(ds, batch_size=4, sampler=SequentialSampler(), as_numpy=False)
         for x, y in iter:
             print(x, y)
     
@@ -146,7 +146,7 @@ class TestCase1(unittest.TestCase):
         num_samples = 1000
         dataset = generate_fake_dataset(num_samples)
         
-        batch = Batch(dataset, batch_size=batch_size, sampler=SequentialSampler())
+        batch = DataSetIter(dataset, batch_size=batch_size, sampler=SequentialSampler())
         for batch_x, batch_y in batch:
             pass
     
diff --git a/test/core/test_callbacks.py b/test/core/test_callbacks.py
index 71a5565d..909295c0 100644
--- a/test/core/test_callbacks.py
+++ b/test/core/test_callbacks.py
@@ -40,89 +40,50 @@ class TestCallback(unittest.TestCase):
     
     def test_gradient_clip(self):
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=20,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          dev_data=data_set,
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          callbacks=[GradientClipCallback(model.parameters(), clip_value=2)])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=20, print_every=50, dev_data=data_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), use_tqdm=False,
+                          callbacks=[GradientClipCallback(model.parameters(), clip_value=2)], check_code_level=2)
         trainer.train()
     
     def test_early_stop(self):
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=20,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.01),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          dev_data=data_set,
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          callbacks=[EarlyStopCallback(5)])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.01), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=20, print_every=50, dev_data=data_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), use_tqdm=False,
+                          callbacks=[EarlyStopCallback(5)], check_code_level=2)
         trainer.train()
     
     def test_lr_scheduler(self):
         data_set, model = prepare_env()
         optimizer = torch.optim.SGD(model.parameters(), lr=0.01)
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=5,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=optimizer,
-                          check_code_level=2,
-                          use_tqdm=False,
-                          dev_data=data_set,
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          callbacks=[LRScheduler(torch.optim.lr_scheduler.StepLR(optimizer, step_size=10, gamma=0.1))])
+        trainer = Trainer(data_set, model, optimizer=optimizer, loss=BCELoss(pred="predict", target="y"), batch_size=32,
+                          n_epochs=5, print_every=50, dev_data=data_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), use_tqdm=False,
+                          callbacks=[LRScheduler(torch.optim.lr_scheduler.StepLR(optimizer, step_size=10, gamma=0.1))],
+                          check_code_level=2)
         trainer.train()
     
     def test_KeyBoardInterrupt(self):
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=5,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          callbacks=[ControlC(False)])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=5, print_every=50, use_tqdm=False, callbacks=[ControlC(False)],
+                          check_code_level=2)
         trainer.train()
     
     def test_LRFinder(self):
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=5,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          callbacks=[LRFinder(len(data_set) // 32)])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=5, print_every=50, use_tqdm=False,
+                          callbacks=[LRFinder(len(data_set) // 32)], check_code_level=2)
         trainer.train()
     
     def test_TensorboardCallback(self):
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=5,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          dev_data=data_set,
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          callbacks=[TensorboardCallback("loss", "metric")])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=5, print_every=50, dev_data=data_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), use_tqdm=False,
+                          callbacks=[TensorboardCallback("loss", "metric")], check_code_level=2)
         trainer.train()
     
     def test_readonly_property(self):
@@ -141,16 +102,9 @@ class TestCallback(unittest.TestCase):
                 print(self.optimizer)
         
         data_set, model = prepare_env()
-        trainer = Trainer(data_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          n_epochs=total_epochs,
-                          batch_size=32,
-                          print_every=50,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=False,
-                          dev_data=data_set,
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          callbacks=[MyCallback()])
+        trainer = Trainer(data_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=total_epochs, print_every=50, dev_data=data_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), use_tqdm=False, callbacks=[MyCallback()],
+                          check_code_level=2)
         trainer.train()
         assert passed_epochs == list(range(1, total_epochs + 1))
diff --git a/test/core/test_metrics.py b/test/core/test_metrics.py
index f3b0178c..9c8a586c 100644
--- a/test/core/test_metrics.py
+++ b/test/core/test_metrics.py
@@ -161,7 +161,15 @@ class TestAccuracyMetric(unittest.TestCase):
             print(e)
             return
         self.assertTrue(True, False), "No exception catches."
-    
+
+    def test_duplicate(self):
+        # 0.4.1的潜在bug，不能出现形参重复的情况
+        metric = AccuracyMetric(pred='predictions', target='targets')
+        pred_dict = {"predictions": torch.zeros(4, 3, 2), "seq_len": torch.ones(4) * 3, 'pred':0}
+        target_dict = {'targets':torch.zeros(4, 3), 'target': 0}
+        metric(pred_dict=pred_dict, target_dict=target_dict)
+
+
     def test_seq_len(self):
         N = 256
         seq_len = torch.zeros(N).long()
diff --git a/test/core/test_trainer.py b/test/core/test_trainer.py
index f559eac5..dc1a531a 100644
--- a/test/core/test_trainer.py
+++ b/test/core/test_trainer.py
@@ -46,18 +46,10 @@ class TrainerTestGround(unittest.TestCase):
         
         model = NaiveClassifier(2, 1)
         
-        trainer = Trainer(train_set, model,
-                          loss=BCELoss(pred="predict", target="y"),
-                          metrics=AccuracyMetric(pred="predict", target="y"),
-                          n_epochs=10,
-                          batch_size=32,
-                          print_every=50,
-                          validate_every=-1,
-                          dev_data=dev_set,
-                          optimizer=SGD(lr=0.1),
-                          check_code_level=2,
-                          use_tqdm=True,
-                          save_path=None)
+        trainer = Trainer(train_set, model, optimizer=SGD(lr=0.1), loss=BCELoss(pred="predict", target="y"),
+                          batch_size=32, n_epochs=10, print_every=50, dev_data=dev_set,
+                          metrics=AccuracyMetric(pred="predict", target="y"), validate_every=-1, save_path=None,
+                          use_tqdm=True, check_code_level=2)
         trainer.train()
         """
         # 应该正确运行
@@ -83,10 +75,7 @@ class TrainerTestGround(unittest.TestCase):
         model = Model()
         
         with self.assertRaises(RuntimeError):
-            trainer = Trainer(
-                train_data=dataset,
-                model=model
-            )
+            trainer = Trainer(train_data=dataset, model=model)
         """
         # 应该获取到的报错提示
         NameError: 
@@ -116,12 +105,7 @@ class TrainerTestGround(unittest.TestCase):
                 return {'loss': loss}
         
         model = Model()
-        trainer = Trainer(
-            train_data=dataset,
-            model=model,
-            use_tqdm=False,
-            print_every=2
-        )
+        trainer = Trainer(train_data=dataset, model=model, print_every=2, use_tqdm=False)
         trainer.train()
         """
         # 应该正确运行
@@ -147,12 +131,7 @@ class TrainerTestGround(unittest.TestCase):
         
         model = Model()
         with self.assertRaises(NameError):
-            trainer = Trainer(
-                train_data=dataset,
-                model=model,
-                use_tqdm=False,
-                print_every=2
-            )
+            trainer = Trainer(train_data=dataset, model=model, print_every=2, use_tqdm=False)
             trainer.train()
     
     def test_trainer_suggestion4(self):
@@ -175,12 +154,7 @@ class TrainerTestGround(unittest.TestCase):
         
         model = Model()
         with self.assertRaises(NameError):
-            trainer = Trainer(
-                train_data=dataset,
-                model=model,
-                use_tqdm=False,
-                print_every=2
-            )
+            trainer = Trainer(train_data=dataset, model=model, print_every=2, use_tqdm=False)
     
     def test_trainer_suggestion5(self):
         # 检查报错提示能否正确提醒用户
@@ -203,12 +177,7 @@ class TrainerTestGround(unittest.TestCase):
                 return {'loss': loss}
         
         model = Model()
-        trainer = Trainer(
-            train_data=dataset,
-            model=model,
-            use_tqdm=False,
-            print_every=2
-        )
+        trainer = Trainer(train_data=dataset, model=model, print_every=2, use_tqdm=False)
     
     def test_trainer_suggestion6(self):
         # 检查报错提示能否正确提醒用户
@@ -233,14 +202,8 @@ class TrainerTestGround(unittest.TestCase):
         
         model = Model()
         with self.assertRaises(NameError):
-            trainer = Trainer(
-                train_data=dataset,
-                model=model,
-                dev_data=dataset,
-                loss=CrossEntropyLoss(),
-                metrics=AccuracyMetric(),
-                use_tqdm=False,
-                print_every=2)
+            trainer = Trainer(train_data=dataset, model=model, loss=CrossEntropyLoss(), print_every=2, dev_data=dataset,
+                              metrics=AccuracyMetric(), use_tqdm=False)
     
     """
     def test_trainer_multiprocess(self):
diff --git a/test/models/model_runner.py b/test/models/model_runner.py
index 405aa7d6..ae589470 100644
--- a/test/models/model_runner.py
+++ b/test/models/model_runner.py
@@ -130,11 +130,8 @@ class ModelRunner():
         tester = Tester(data=data, model=model, metrics=metrics,
                         batch_size=BATCH_SIZE, verbose=0)
         before_train = tester.test()
-        trainer = Trainer(model=model, train_data=data, dev_data=None,
-                          n_epochs=N_EPOCHS, batch_size=BATCH_SIZE,
-                          loss=loss,
-                          save_path=None,
-                          use_tqdm=False)
+        trainer = Trainer(train_data=data, model=model, loss=loss, batch_size=BATCH_SIZE, n_epochs=N_EPOCHS,
+                          dev_data=None, save_path=None, use_tqdm=False)
         trainer.train(load_best_model=False)
         after_train = tester.test()
         for metric_name, v1 in before_train.items():
diff --git a/test/models/test_biaffine_parser.py b/test/models/test_biaffine_parser.py
index e6fca6a8..4f93b994 100644
--- a/test/models/test_biaffine_parser.py
+++ b/test/models/test_biaffine_parser.py
@@ -1,6 +1,5 @@
 import unittest
 
-import fastNLP
 from fastNLP.models.biaffine_parser import BiaffineParser, ParserLoss, ParserMetric
 from .model_runner import *
 
diff --git a/test/modules/decoder/test_CRF.py b/test/modules/decoder/test_CRF.py
index 5dec7d47..647af7d3 100644
--- a/test/modules/decoder/test_CRF.py
+++ b/test/modules/decoder/test_CRF.py
@@ -10,14 +10,14 @@ class TestCRF(unittest.TestCase):
         id2label = {0: 'B', 1: 'I', 2:'O'}
         expected_res = {(0, 0), (0, 1), (0, 2), (0, 4), (1, 0), (1, 1), (1, 2), (1, 4), (2, 0), (2, 2),
                         (2, 4), (3, 0), (3, 2)}
-        self.assertSetEqual(expected_res, set(allowed_transitions(id2label)))
+        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, include_start_end=True)))
 
         id2label = {0: 'B', 1:'M', 2:'E', 3:'S'}
         expected_res = {(0, 1), (0, 2), (1, 1), (1, 2), (2, 0), (2, 3), (2, 5), (3, 0), (3, 3), (3, 5), (4, 0), (4, 3)}
-        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, encoding_type='BMES')))
+        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, encoding_type='BMES', include_start_end=True)))
 
         id2label = {0: 'B', 1: 'I', 2:'O', 3: '<pad>', 4:"<unk>"}
-        allowed_transitions(id2label)
+        allowed_transitions(id2label, include_start_end=True)
 
         labels = ['O']
         for label in ['X', 'Y']:
@@ -27,7 +27,7 @@ class TestCRF(unittest.TestCase):
         expected_res = {(0, 0), (0, 1), (0, 3), (0, 6), (1, 0), (1, 1), (1, 2), (1, 3), (1, 6), (2, 0), (2, 1),
                         (2, 2), (2, 3), (2, 6), (3, 0), (3, 1), (3, 3), (3, 4), (3, 6), (4, 0), (4, 1), (4, 3),
                         (4, 4), (4, 6), (5, 0), (5, 1), (5, 3)}
-        self.assertSetEqual(expected_res, set(allowed_transitions(id2label)))
+        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, include_start_end=True)))
 
         labels = []
         for label in ['X', 'Y']:
@@ -37,7 +37,7 @@ class TestCRF(unittest.TestCase):
         expected_res = {(0, 1), (0, 2), (1, 1), (1, 2), (2, 0), (2, 3), (2, 4), (2, 7), (2, 9), (3, 0), (3, 3), (3, 4),
                         (3, 7), (3, 9), (4, 5), (4, 6), (5, 5), (5, 6), (6, 0), (6, 3), (6, 4), (6, 7), (6, 9), (7, 0),
                         (7, 3), (7, 4), (7, 7), (7, 9), (8, 0), (8, 3), (8, 4), (8, 7)}
-        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, encoding_type='BMES')))
+        self.assertSetEqual(expected_res, set(allowed_transitions(id2label, encoding_type='BMES', include_start_end=True)))
 
     def test_case2(self):
         # 测试CRF能否避免解码出非法跃迁, 使用allennlp做了验证。
diff --git a/test/test_tutorials.py b/test/test_tutorials.py
index 2e971a4f..87910c3d 100644
--- a/test/test_tutorials.py
+++ b/test/test_tutorials.py
@@ -60,10 +60,10 @@ class TestTutorial(unittest.TestCase):
         print(test_data[0])
 
         # 如果你们需要做强化学习或者GAN之类的项目，你们也可以使用这些数据预处理的工具
-        from fastNLP.core.batch import Batch
+        from fastNLP.core.batch import DataSetIter
         from fastNLP.core.sampler import RandomSampler
 
-        batch_iterator = Batch(dataset=train_data, batch_size=2, sampler=RandomSampler())
+        batch_iterator = DataSetIter(dataset=train_data, batch_size=2, sampler=RandomSampler())
         for batch_x, batch_y in batch_iterator:
             print("batch_x has: ", batch_x)
             print("batch_y has: ", batch_y)
@@ -85,12 +85,8 @@ class TestTutorial(unittest.TestCase):
         # 实例化Trainer，传入模型和数据，进行训练
         # 先在test_data拟合（确保模型的实现是正确的）
         copy_model = deepcopy(model)
-        overfit_trainer = Trainer(model=copy_model, train_data=test_data, dev_data=test_data,
-                                  loss=loss,
-                                  metrics=metric,
-                                  save_path=None,
-                                  batch_size=32,
-                                  n_epochs=5)
+        overfit_trainer = Trainer(train_data=test_data, model=copy_model, loss=loss, batch_size=32, n_epochs=5,
+                                  dev_data=test_data, metrics=metric, save_path=None)
         overfit_trainer.train()
 
         # 用train_data训练，在test_data验证
@@ -147,13 +143,8 @@ class TestTutorial(unittest.TestCase):
 
         from fastNLP import Trainer, CrossEntropyLoss, AccuracyMetric, Adam
 
-        trainer = Trainer(model=model,
-                          train_data=train_data,
-                          dev_data=dev_data,
-                          loss=CrossEntropyLoss(),
-                          optimizer= Adam(),
-                          metrics=AccuracyMetric(target='target')
-                          )
+        trainer = Trainer(train_data=train_data, model=model, optimizer=Adam(), loss=CrossEntropyLoss(),
+                          dev_data=dev_data, metrics=AccuracyMetric(target='target'))
         trainer.train()
         print('Train finished!')