diff --git a/fastNLP/modules/encoder/transformer.py b/fastNLP/modules/encoder/transformer.py
index d29a10c3..3d97c306 100644
--- a/fastNLP/modules/encoder/transformer.py
+++ b/fastNLP/modules/encoder/transformer.py
@@ -40,6 +40,8 @@ class TransformerEncoder(nn.Module):
             :param seq_mask: [batch, seq_len]
             :return: [batch, seq_len, model_size]
             """
+            if seq_mask is None:  # 防止后续乘法时出错
+                seq_mask = 1
             input = self.norm1(input)
             attention = self.atte(input, input, input, atte_mask_out)
             input = input + self.dropout(attention)