diff --git a/paddlespeech/s2t/exps/u2/model.py b/paddlespeech/s2t/exps/u2/model.py
index 5ce5f50bf..66b95f63c 100644
--- a/paddlespeech/s2t/exps/u2/model.py
+++ b/paddlespeech/s2t/exps/u2/model.py
@@ -482,10 +482,12 @@ class U2Tester(U2Trainer):
         # TODO: 80(feature dim) be configable
         input_spec = [
             paddle.static.InputSpec(shape=[1, None, 80], dtype='float32'),
-            paddle.static.InputSpec(shape=[1], dtype='int32'), -1,
+            paddle.static.InputSpec(shape=[1], dtype='int32'), 
+            -1,
             paddle.static.InputSpec(
                 shape=[None, None, None, None],
-                dtype='float32'), paddle.static.InputSpec(
+                dtype='float32'), 
+            paddle.static.InputSpec(
                     shape=[None, None, None, None], dtype='float32')
         ]
         infer_model.forward_encoder_chunk = paddle.jit.to_static(
@@ -511,7 +513,7 @@ class U2Tester(U2Trainer):
         infer_model.ctc_activation = paddle.jit.to_static(
             infer_model.ctc_activation, input_spec=input_spec)
 
-        paddle.jit.save(infer_model, './export.jit', combine_params=True)
+        paddle.jit.save(infer_model, './export.jit', combine_params=True, skip_forward=True)
 
         def flatten(out):
             if isinstance(out, paddle.Tensor):
@@ -531,33 +533,20 @@ class U2Tester(U2Trainer):
         att_cache = paddle.zeros([0, 0, 0, 0])
         cnn_cache = paddle.zeros([0, 0, 0, 0])
 
-        # xs, att_cache, cnn_cache = infer_model.forward_encoder_chunk(xs1, offset, required_cache_size, att_cache, cnn_cache)
-        # xs2 = paddle.rand(shape=[1, 67, 80], dtype='float32')
-        # offset = paddle.to_tensor([16], dtype='int32')
-        # out1 = infer_model.forward_encoder_chunk(xs2, offset, required_cache_size, att_cache, cnn_cache)
-        # print(out1)
-
-        xs, att_cache, cnn_cache = infer_model.forward_encoder_chunk(
-            xs1, offset, att_cache, cnn_cache)
+        xs, att_cache, cnn_cache = infer_model.forward_encoder_chunk(xs1, offset, required_cache_size, att_cache, cnn_cache)
         xs2 = paddle.rand(shape=[1, 67, 80], dtype='float32')
         offset = paddle.to_tensor([16], dtype='int32')
-        out1 = infer_model.forward_encoder_chunk(xs2, offset, att_cache,
-                                                 cnn_cache)
-        print(out1)
-
-        # from paddle.jit.layer import Layer
-        # layer = Layer()
-        # layer.load('./export.jit', paddle.CPUPlace())
-
-        # offset = paddle.to_tensor([0], dtype='int32')
-        # att_cache = paddle.zeros([0, 0, 0, 0])
-        # cnn_cache=paddle.zeros([0, 0, 0, 0])
-        # xs, att_cache, cnn_cache = layer.forward_encoder_chunk(xs1, offset, att_cache, cnn_cache)
-        # offset = paddle.to_tensor([16], dtype='int32')
-        # out2 = layer.forward_encoder_chunk(xs2, offset, att_cache, cnn_cache)
-        # # print(out2)
-
-        # out1 = flatten(out1)
-        # out2 = flatten(out2)
-        # for i in range(len(out1)):
-        #     print(np.equal(out1[i].numpy(), out2[i].numpy()).all())
+        out1 = infer_model.forward_encoder_chunk(xs2, offset, required_cache_size, att_cache, cnn_cache)
+        print('py encoder', out1)
+
+        from paddle.jit.layer import Layer
+        layer = Layer()
+        layer.load('./export.jit', paddle.CPUPlace())
+
+        xs1 = paddle.full([1, 7, 80], 0.1, dtype='float32')
+        offset = paddle.to_tensor([0], dtype='int32')
+        att_cache = paddle.zeros([0, 0, 0, 0])
+        cnn_cache=paddle.zeros([0, 0, 0, 0])
+        func = getattr(layer, 'forward_encoder_chunk')
+        xs, att_cache, cnn_cache = func(xs1, offset, att_cache, cnn_cache)
+        print('py static encoder', xs)
diff --git a/paddlespeech/s2t/models/u2/u2.py b/paddlespeech/s2t/models/u2/u2.py
index e4c667e00..a1daccf18 100644
--- a/paddlespeech/s2t/models/u2/u2.py
+++ b/paddlespeech/s2t/models/u2/u2.py
@@ -924,10 +924,6 @@ class U2InferModel(U2Model):
     def __init__(self, configs: dict):
         super().__init__(configs)
 
-    @jit.to_static(input_spec=[
-        paddle.static.InputSpec(shape=[1, 1, 1], dtype='int64'),
-        paddle.static.InputSpec(shape=[1], dtype='int64')
-    ])
     def forward(self,
                 feats,
                 feats_lengths,
diff --git a/paddlespeech/s2t/modules/encoder.py b/paddlespeech/s2t/modules/encoder.py
index bff2d69bb..a7919bca4 100644
--- a/paddlespeech/s2t/modules/encoder.py
+++ b/paddlespeech/s2t/modules/encoder.py
@@ -251,10 +251,11 @@ class BaseEncoder(nn.Layer):
         for i, layer in enumerate(self.encoders):
             # att_cache[i:i+1] = (1, head, cache_t1, d_k*2)
             # cnn_cache[i:i+1] = (1, B=1, hidden-dim, cache_t2)
+            # zeros([0,0,0,0]) support [i:i+1] slice
             xs, _, new_att_cache, new_cnn_cache = layer(
                 xs, att_mask, pos_emb,
-                att_cache=att_cache[i:i+1] if elayers > 0 else att_cache,
-                cnn_cache=cnn_cache[i:i+1] if paddle.shape(cnn_cache)[0] > 0 else cnn_cache,
+                att_cache=att_cache[i:i+1],
+                cnn_cache=cnn_cache[i:i+1],
             )
             # new_att_cache = (1, head, attention_key_size, d_k*2)
             # new_cnn_cache = (B=1, hidden-dim, cache_t2)