I have solved the problem. According to https://discuss.pennylane.ai/t/quantum-neural-networks-quanvolutional-nn/1111/7 and https://discuss.pennylane.ai/t/transfer-learning-with-pretrained-keras-model/1462/10. I add this code
model(X_train[:2])
behind
model = keras.Model(inputs=input, outputs=output)
Althought I don’t know the reason, it works. 