diff --git a/fastNLP/core/tester.py b/fastNLP/core/tester.py
index 5495dbec..919554c5 100644
--- a/fastNLP/core/tester.py
+++ b/fastNLP/core/tester.py
@@ -1,10 +1,11 @@
+import itertools
 from collections import defaultdict
 
 import torch
 
 from fastNLP.core.batch import Batch
 from fastNLP.core.sampler import RandomSampler
-
+from fastNLP.core.utils import _build_args
 
 class Tester(object):
     """An collection of model inference and evaluation of performance, used over validation/dev set and test set. """
@@ -40,7 +41,12 @@ class Tester(object):
                     output[k].append(v)
                 for k, v in batch_y.items():
                     truths[k].append(v)
-            eval_results = self.evaluate(**output, **truths)
+            for k, v in output.items():
+                output[k] = itertools.chain(*v)
+            for k, v in truths.items():
+                truths[k] = itertools.chain(*v)
+            args = _build_args(self._evaluator, **output, **truths)
+            eval_results = self._evaluator(**args)
         print("[tester] {}".format(self.print_eval_results(eval_results)))
         self.mode(network, is_test=False)
         self.metrics = eval_results
@@ -60,14 +66,10 @@ class Tester(object):
 
     def data_forward(self, network, x):
         """A forward pass of the model. """
+        x = _build_args(network.forward, **x)
         y = network(**x)
         return y
 
-    def evaluate(self, **kwargs):
-        """Compute evaluation metrics.
-        """
-        return self._evaluator(**kwargs)
-
     def print_eval_results(self, results):
         """Override this method to support more print formats.
 
diff --git a/fastNLP/core/trainer.py b/fastNLP/core/trainer.py
index 2a6458c6..a21f2ded 100644
--- a/fastNLP/core/trainer.py
+++ b/fastNLP/core/trainer.py
@@ -21,9 +21,8 @@ class Trainer(object):
 
     """
    def __init__(self, train_data, model, n_epochs=3, batch_size=32, print_every=-1,
-                 dev_data=None, use_cuda=False, loss=Loss(None), save_path="./save",
+                 dev_data=None, use_cuda=False, save_path="./save",
                  optimizer=Optimizer("Adam", lr=0.001, weight_decay=0),
-                 evaluator=Evaluator(),
                  **kwargs):
         super(Trainer, self).__init__()
 
@@ -36,9 +35,16 @@ class Trainer(object):
         self.save_path = str(save_path)
         self.print_every = int(print_every)
 
-        self.loss_func = self.model.loss if hasattr(self.model, "loss") else loss.get()
-        self.optimizer = optimizer.construct_from_pytorch(self.model.parameters())
-        self.evaluator = evaluator
+        model_name = model.__class__.__name__
+        assert hasattr(self.model, 'get_loss'), "model {} has to have a 'get_loss' function.".format(model_name)
+        self.loss_func = self.model.get_loss
+        if isinstance(optimizer, torch.optim.Optimizer):
+            self.optimizer = optimizer
+        else:
+            self.optimizer = optimizer.construct_from_pytorch(self.model.parameters())
+
+        assert hasattr(self.model, 'evaluate'), "model {} has to have a 'evaluate' function.".format(model_name)
+        self.evaluator = self.model.evaluate
 
         if self.dev_data is not None:
             valid_args = {"batch_size": self.batch_size, "save_path": self.save_path,
@@ -48,7 +54,10 @@ class Trainer(object):
         for k, v in kwargs.items():
             setattr(self, k, v)
 
-        self._summary_writer = SummaryWriter(os.path.join(self.save_path, 'tensorboard_logs'))
+        self.tensorboard_path = os.path.join(self.save_path, 'tensorboard_logs')
+        if os.path.exists(self.tensorboard_path):
+            os.rmdir(self.tensorboard_path)
+        self._summary_writer = SummaryWriter(self.tensorboard_path)
         self._graph_summaried = False
         self.step = 0
         self.start_time = None  # start timestamp
@@ -138,6 +147,7 @@ class Trainer(object):
         self.optimizer.step()
 
     def data_forward(self, network, x):
+        x = _build_args(network.forward, **x)
         y = network(**x)
         if not self._graph_summaried:
             # self._summary_writer.add_graph(network, x, verbose=False)
@@ -161,12 +171,9 @@ class Trainer(object):
         :param truth: ground truth label vector
         :return: a scalar
         """
-        if isinstance(predict, dict) and isinstance(truth, dict):
-            return self.loss_func(**predict, **truth)
-        if len(truth) > 1:
-            raise NotImplementedError("Not ready to handle multi-labels.")
-        truth = list(truth.values())[0] if len(truth) > 0 else None
-        return self.loss_func(predict, truth)
+        assert isinstance(predict, dict) and isinstance(truth, dict)
+        args = _build_args(self.loss_func, **predict, **truth)
+        return self.loss_func(**args)
 
     def save_model(self, model, model_name, only_param=False):
         model_name = os.path.join(self.save_path, model_name)
diff --git a/fastNLP/models/cnn_text_classification.py b/fastNLP/models/cnn_text_classification.py
index e814717b..04f0c6d9 100644
--- a/fastNLP/models/cnn_text_classification.py
+++ b/fastNLP/models/cnn_text_classification.py
@@ -46,5 +46,18 @@ class CNNText(torch.nn.Module):
         x = self.fc(x)  # [N,C] -> [N, N_class]
         return {'output':x}
 
-    def loss(self, output, label_seq):
+    def predict(self, word_seq):
+        output = self(word_seq)
+        _, predict = output.max(dim=1)
+        return {'predict': predict}
+
+    def get_loss(self, output, label_seq):
         return self._loss(output, label_seq)
+
+    def evaluate(self, predict, label_seq):
+        predict, label_seq = torch.stack(predict, dim=0), torch.stack(label_seq, dim=0)
+        predict, label_seq = predict.squeeze(), label_seq.squeeze()
+        correct = (predict == label_seq).long().sum().item()
+        total = label_seq.size(0)
+        return 1.0 * correct / total
+