I almost forgot about this question.I still don’t know what caused this problem.
However, I normalized the original data and got a good result.
I try to use the LSTM + Linear structure to train and predict the function y = X,
Only by normalizing x can I get good prediction results
so，I cant understand  why normalization  can be useful？ I think it just a method to shrink data.
Maybe I didn’t find the crux of the problem at all.