Thanks your reply. @ptrblck
Yes, the returned loss of two reduction way are same, which is 0.7351 at the first time.
When I rerun the reduction with none, it always show 0.7351 at the first time.
I confirmed it by using ipdb to check.
But after several iteration, the loss began to differ.
So,  How to fix the calculation order of reduction.
The reason why I wanna convert to reduction of none, is that I wanna combine sample weight to existed class weight’s loss.