diff --git a/fastNLP/api/api.py b/fastNLP/api/api.py
index 823e0ee0..4198fd2b 100644
--- a/fastNLP/api/api.py
+++ b/fastNLP/api/api.py
@@ -5,17 +5,25 @@ from fastNLP.core.dataset import DataSet
 from fastNLP.core.instance import Instance
 from fastNLP.core.predictor import Predictor
 
+from fastNLP.api.model_zoo import load_url
+
+model_urls = {
+    'cws': "",
+
+}
+
 
 class API:
     def __init__(self):
         self.pipeline = None
-        self.model = None
 
     def predict(self, *args, **kwargs):
         raise NotImplementedError
 
-    def load(self, name):
-        _dict = torch.load(name)
+    def load(self, path):
+
+
+        _dict = torch.load(path)
         self.pipeline = _dict['pipeline']
 
 
@@ -61,8 +69,13 @@ class POS_tagger(API):
 
 
 class CWS(API):
-    def __init__(self, model_path='xxx'):
+    def __init__(self, model_path=None, pretrain=True):
         super(CWS, self).__init__()
+        # 1. 这里修改为检查
+        if model_path is None:
+            model_path = model_urls['cws']
+
+
         self.load(model_path)
 
     def predict(self, sentence, pretrain=False):
@@ -94,3 +107,6 @@ class CWS(API):
 if __name__ == "__main__":
     tagger = POS_tagger()
     print(tagger.predict([["我", "是", "学生", "。"], ["我", "是", "学生", "。"]]))
+
+    from torchvision import models
+    models.resnet18()
diff --git a/fastNLP/api/model_zoo.py b/fastNLP/api/model_zoo.py
new file mode 100644
index 00000000..fcfc966e
--- /dev/null
+++ b/fastNLP/api/model_zoo.py
@@ -0,0 +1,138 @@
+import torch
+
+import hashlib
+import os
+import re
+import shutil
+import sys
+import tempfile
+
+try:
+    from requests.utils import urlparse
+    from requests import get as urlopen
+    requests_available = True
+except ImportError:
+    requests_available = False
+    if sys.version_info[0] == 2:
+        from urlparse import urlparse  # noqa f811
+        from urllib2 import urlopen  # noqa f811
+    else:
+        from urllib.request import urlopen
+        from urllib.parse import urlparse
+try:
+    from tqdm import tqdm
+except ImportError:
+    tqdm = None  # defined below
+
+# matches bfd8deac from resnet18-bfd8deac.pth
+HASH_REGEX = re.compile(r'-([a-f0-9]*)\.')
+
+
+def load_url(url, model_dir=None, map_location=None, progress=True):
+    r"""Loads the Torch serialized object at the given URL.
+
+    If the object is already present in `model_dir`, it's deserialized and
+    returned. The filename part of the URL should follow the naming convention
+    ``filename-<sha256>.ext`` where ``<sha256>`` is the first eight or more
+    digits of the SHA256 hash of the contents of the file. The hash is used to
+    ensure unique names and to verify the contents of the file.
+
+    The default value of `model_dir` is ``$TORCH_HOME/models`` where
+    ``$TORCH_HOME`` defaults to ``~/.torch``. The default directory can be
+    overridden with the ``$TORCH_MODEL_ZOO`` environment variable.
+
+    Args:
+        url (string): URL of the object to download
+        model_dir (string, optional): directory in which to save the object
+        map_location (optional): a function or a dict specifying how to remap storage locations (see torch.load)
+        progress (bool, optional): whether or not to display a progress bar to stderr
+
+    Example:
+        # >>> state_dict = model_zoo.load_url('https://s3.amazonaws.com/pytorch/models/resnet18-5c106cde.pth')
+
+    """
+    if model_dir is None:
+        torch_home = os.path.expanduser(os.getenv('fastNLP_HOME', '~/.fastNLP'))
+        model_dir = os.getenv('fastNLP_MODEL_ZOO', os.path.join(torch_home, 'models'))
+    if not os.path.exists(model_dir):
+        os.makedirs(model_dir)
+    parts = urlparse(url)
+    filename = os.path.basename(parts.path)
+    cached_file = os.path.join(model_dir, filename)
+    if not os.path.exists(cached_file):
+        sys.stderr.write('Downloading: "{}" to {}\n'.format(url, cached_file))
+        # hash_prefix = HASH_REGEX.search(filename).group(1)
+        _download_url_to_file(url, cached_file, hash_prefix=None, progress=progress)
+    return torch.load(cached_file, map_location=map_location)
+
+
+def _download_url_to_file(url, dst, hash_prefix, progress):
+    if requests_available:
+        u = urlopen(url, stream=True)
+        file_size = int(u.headers["Content-Length"])
+        u = u.raw
+    else:
+        u = urlopen(url)
+        meta = u.info()
+        if hasattr(meta, 'getheaders'):
+            file_size = int(meta.getheaders("Content-Length")[0])
+        else:
+            file_size = int(meta.get_all("Content-Length")[0])
+
+    f = tempfile.NamedTemporaryFile(delete=False)
+    try:
+        if hash_prefix is not None:
+            sha256 = hashlib.sha256()
+        with tqdm(total=file_size, disable=not progress) as pbar:
+            while True:
+                buffer = u.read(8192)
+                if len(buffer) == 0:
+                    break
+                f.write(buffer)
+                if hash_prefix is not None:
+                    sha256.update(buffer)
+                pbar.update(len(buffer))
+
+        f.close()
+        if hash_prefix is not None:
+            digest = sha256.hexdigest()
+            if digest[:len(hash_prefix)] != hash_prefix:
+                raise RuntimeError('invalid hash value (expected "{}", got "{}")'
+                                   .format(hash_prefix, digest))
+        shutil.move(f.name, dst)
+    finally:
+        f.close()
+        if os.path.exists(f.name):
+            os.remove(f.name)
+
+
+if tqdm is None:
+    # fake tqdm if it's not installed
+    class tqdm(object):
+
+        def __init__(self, total, disable=False):
+            self.total = total
+            self.disable = disable
+            self.n = 0
+
+        def update(self, n):
+            if self.disable:
+                return
+
+            self.n += n
+            sys.stderr.write("\r{0:.1f}%".format(100 * self.n / float(self.total)))
+            sys.stderr.flush()
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc_val, exc_tb):
+            if self.disable:
+                return
+
+            sys.stderr.write('\n')
+
+
+if __name__ == '__main__':
+    pipeline = load_url('http://10.141.208.102:5000/file/download/infer_context.pkl', model_dir='.')
+    print(type(pipeline))
diff --git a/fastNLP/core/sampler.py b/fastNLP/core/sampler.py
index 652bc97e..6ba2f4d3 100644
--- a/fastNLP/core/sampler.py
+++ b/fastNLP/core/sampler.py
@@ -45,14 +45,14 @@ class RandomSampler(BaseSampler):
 
 class BucketSampler(BaseSampler):
 
-    def __init__(self, num_buckets=10, batch_size=32):
+    def __init__(self, num_buckets=10, batch_size=32, seq_lens_field_name='seq_lens'):
         self.num_buckets = num_buckets
         self.batch_size = batch_size
+        self.seq_lens_field_name = seq_lens_field_name
 
     def __call__(self, data_set):
-        assert 'seq_lens' in data_set, "BuckectSampler only support data_set with seq_lens right now."
 
-        seq_lens = data_set['seq_lens'].content
+        seq_lens = data_set[self.seq_lens_field_name].content
         total_sample_num = len(seq_lens)
 
         bucket_indexes = []