diff --git a/paddlespeech/s2t/exps/u2/bin/test_wav.py b/paddlespeech/s2t/exps/u2/bin/test_wav.py
index a6228a128..0d1a3b3cc 100644
--- a/paddlespeech/s2t/exps/u2/bin/test_wav.py
+++ b/paddlespeech/s2t/exps/u2/bin/test_wav.py
@@ -78,7 +78,7 @@ class U2Infer():
             if self.args.debug:
                 np.savetxt("feat.transform.txt", feat)
 
-            ilen = paddle.to_tensor(feat.shape[0])
+            ilen = paddle.to_tensor(feat.shape[0]).unsqueeze(0)
             xs = paddle.to_tensor(feat, dtype='float32').unsqueeze(0)
             decode_config = self.config.decode
             logger.info(f"decode cfg: {decode_config}")