diff --git a/fastNLP/core/vocabulary.py b/fastNLP/core/vocabulary.py
index 5d9f2185..2f2358a1 100644
--- a/fastNLP/core/vocabulary.py
+++ b/fastNLP/core/vocabulary.py
@@ -1,4 +1,5 @@
 from copy import deepcopy
+from collections import Counter
 
 DEFAULT_PADDING_LABEL = '<pad>'  # dict index = 0
 DEFAULT_UNKNOWN_LABEL = '<unk>'  # dict index = 1
@@ -23,9 +24,6 @@ def check_build_vocab(func):
     def _wrapper(self, *args, **kwargs):
         if self.word2idx is None:
             self.build_vocab()
-            self.build_reverse_vocab()
-        elif self.idx2word is None:
-            self.build_reverse_vocab()
         return func(self, *args, **kwargs)
     return _wrapper
 
@@ -49,7 +47,7 @@ class Vocabulary(object):
         """
         self.max_size = max_size
         self.min_freq = min_freq
-        self.word_count = {}
+        self.word_count = Counter()
         self.has_default = need_default
         if self.has_default:
             self.padding_label = DEFAULT_PADDING_LABEL
@@ -71,13 +69,14 @@ class Vocabulary(object):
                 self.update(w)
         else:
         # it's a word to be added
-            if word not in self.word_count:
-                self.word_count[word] = 1
-            else:
-                self.word_count[word] += 1
+            self.word_count[word] += 1
             self.word2idx = None
         return self
 
+    def update_list(self, sent):
+        self.word_count.update(sent)
+        self.word2idx = None
+
     def build_vocab(self):
         """build 'word to index' dict, and filter the word using `max_size` and `min_freq`
         """
@@ -88,26 +87,25 @@ class Vocabulary(object):
         else:
             self.word2idx = {}
 
-        words = sorted(self.word_count.items(), key=lambda kv: kv[1], reverse=True)
+        max_size = min(self.max_size, len(self.word_count)) if self.max_size else None
+        words = self.word_count.most_common(max_size)
         if self.min_freq is not None:
-            words = list(filter(lambda kv: kv[1] >= self.min_freq, words))
-        if self.max_size is not None and len(words) > self.max_size:
-            words = words[:self.max_size]
-        for w, _ in words:
-            self.word2idx[w] = len(self.word2idx)
+            words = filter(lambda kv: kv[1] >= self.min_freq, words)
+        start_idx = len(self.word2idx)
+        self.word2idx.update({w:i+start_idx for i, (w,_) in enumerate(words)})
+        self.build_reverse_vocab()
 
     def build_reverse_vocab(self):
         """build 'index to word' dict based on 'word to index' dict
         """
-        self.idx2word = {self.word2idx[w] : w for w in self.word2idx}
+        self.idx2word = {i: w for w, i in self.word2idx.items()}
 
     @check_build_vocab
     def __len__(self):
         return len(self.word2idx)
 
-    @check_build_vocab
     def has_word(self, w):
-        return w in self.word2idx
+        return self.__contains__(w)
 
     @check_build_vocab
     def __getitem__(self, w):
@@ -122,14 +120,13 @@ class Vocabulary(object):
         else:
             raise ValueError("word {} not in vocabulary".format(w))
 
-    @check_build_vocab
     def to_index(self, w):
         """ like to_index(w) function, turn a word to the index
             if w is not in Vocabulary, return the unknown label
 
         :param str w:
         """
-        return self[w]
+        return self.__getitem__(w)
 
     @property
     @check_build_vocab
@@ -140,7 +137,7 @@ class Vocabulary(object):
 
     def __setattr__(self, name, val):
         self.__dict__[name] = val
-        if name in self.__dict__ and name in ["unknown_label", "padding_label"]:
+        if name in ["unknown_label", "padding_label"]:
             self.word2idx = None
 
     @property
@@ -156,8 +153,6 @@ class Vocabulary(object):
 
         :param int idx:
         """
-        if self.idx2word is None:
-            self.build_reverse_vocab()
         return self.idx2word[idx]
 
     def __getstate__(self):
@@ -172,12 +167,13 @@ class Vocabulary(object):
         """use to restore state from pickle
         """
         self.__dict__.update(state)
-        self.idx2word = None
+        self.build_reverse_vocab()
 
+    @check_build_vocab
     def __contains__(self, item):
         """Check if a word in vocabulary.
 
         :param item: the word
         :return: True or False
         """
-        return self.has_word(item)
+        return item in self.word2idx
diff --git a/fastNLP/io/base_loader.py b/fastNLP/io/base_loader.py
index fc2814c8..2cdfcab4 100644
--- a/fastNLP/io/base_loader.py
+++ b/fastNLP/io/base_loader.py
@@ -1,3 +1,6 @@
+import os
+import _pickle as pickle
+
 class BaseLoader(object):
 
     def __init__(self):
@@ -9,12 +12,23 @@ class BaseLoader(object):
             text = f.readlines()
         return [line.strip() for line in text]
 
-    @staticmethod
-    def load(data_path):
+    @classmethod
+    def load(cls, data_path):
         with open(data_path, "r", encoding="utf-8") as f:
             text = f.readlines()
         return [[word for word in sent.strip()] for sent in text]
 
+    @classmethod
+    def load_with_cache(cls, data_path, cache_path):
+        if os.path.isfile(cache_path) and os.path.getmtime(data_path) < os.path.getmtime(cache_path):
+            with open(cache_path, 'rb') as f:
+                return pickle.load(f)
+        else:
+            obj = cls.load(data_path)
+            with open(cache_path, 'wb') as f:
+                pickle.dump(obj, f)
+            return obj
+
 
 class ToyLoader0(BaseLoader):
     """