diff --git a/fastNLP/modules/encoder/_elmo.py b/fastNLP/modules/encoder/_elmo.py
index 11feead6..ab43d32f 100644
--- a/fastNLP/modules/encoder/_elmo.py
+++ b/fastNLP/modules/encoder/_elmo.py
@@ -761,11 +761,11 @@ class _ElmoModel(nn.Module):
             token_embedding = self.token_embedder(expanded_words, chars)
         if self.config['encoder']['name'] == 'elmo':
             encoder_output = self.encoder(token_embedding, seq_len)
-            if encoder_output.size(2) < max_len:
+            if encoder_output.size(2) < max_len+2:
                 dummy_tensor = encoder_output.new_zeros(encoder_output.size(0), batch_size,
-                                                        max_len - encoder_output.size(2), encoder_output.size(-1))
+                                                        max_len + 2 - encoder_output.size(2), encoder_output.size(-1))
                 encoder_output = torch.cat([encoder_output, dummy_tensor], 2)
-            sz = encoder_output.size()  # batch_size, max_len, hidden_size
+            sz = encoder_output.size()  # 2, batch_size, max_len, hidden_size
             token_embedding = torch.cat([token_embedding, token_embedding], dim=2).view(1, sz[1], sz[2], sz[3])
             encoder_output = torch.cat([token_embedding, encoder_output], dim=0)
         elif self.config['encoder']['name'] == 'lstm':