diff --git a/fastNLP/io/data_loader/sst.py b/fastNLP/io/data_loader/sst.py
index 0d881e65..6c06a9ce 100644
--- a/fastNLP/io/data_loader/sst.py
+++ b/fastNLP/io/data_loader/sst.py
@@ -134,6 +134,7 @@ class SST2Loader(CSVLoader):
         info = DataBundle()
         for name, path in paths.items():
             dataset = self.load(path)
+            dataset.apply_field(lambda words:words.copy(), field_name='words', new_field_name='raw_words')
             datasets[name] = dataset
 
         def wordtochar(words):