diff --git a/paddlespeech/s2t/models/u2/u2.py b/paddlespeech/s2t/models/u2/u2.py
index ca83ca17046dd016d76c8f9bf873c711e3448635..e4c667e00199d2956664f9de32afe86c21243ef4 100644
--- a/paddlespeech/s2t/models/u2/u2.py
+++ b/paddlespeech/s2t/models/u2/u2.py
@@ -654,7 +654,7 @@ class U2BaseModel(ASRInterface, nn.Layer):
         Args:
             xs (paddle.Tensor): encoder output, (B, T, D)
         Returns:
-            paddle.Tensor: activation before ctc
+            paddle.Tensor: activation before ctc. (B, Tmax, odim)
         """
         return self.ctc.log_softmax(xs)