Thank u for your help.
The reason you didn’t meet the problem I mentioned may be that u didn’t run this model in more than one batchs.
I test this morning, if I use “for image, target in dataset:” or "for i in range(100):"I will get exactly same features, like this:

Untitled1661×379 63.6 KB

So I just simply choose one of those same features.And I carefully check my code.
To some extent, I have solved my problem , but I have no idea how this happens, can u explain to me if u are interested?Thanks!