diff --git a/paddle/fluid/operators/rnn_op.h b/paddle/fluid/operators/rnn_op.h
index 253765bb41940a5f62874df95e8a110b5d853b3d..b993f5ac17479544e127f669c94ce0606ab47399 100644
--- a/paddle/fluid/operators/rnn_op.h
+++ b/paddle/fluid/operators/rnn_op.h
@@ -960,9 +960,10 @@ class RNNCPUKernel : public framework::OpKernel<T> {
     if (has_seq_length) {
       sequence_length = ctx.Input<Tensor>("SequenceLength");
     }
-    if (!dropout_mask->IsInitialized()) {
-      dropout_mask->mutable_data<uint8_t>(output->dims(), ctx.GetPlace());
+    if (dropout_mask->IsInitialized()) {
+      if (dropout_mask->numel() != output->numel()) dropout_mask->clear();
     }
+    dropout_mask->mutable_data<uint8_t>(output->dims(), ctx.GetPlace());
 
     // init the output and allocate the memory
     output->mutable_data<T>(ctx.GetPlace());