Thank you.
I changed image, byte tensor to float tensor
and lables, byte tensor to long tensor like
data['image'].float()
data['labels'].long()

but another Run time error happened at loss calculation.
Runtime Error:  multi-target not supported at /opt/conda/conda-bld/pytorch_1503965122592/work/torch/lib/THNN/generic/ClassNLLCriterion.c:22 

outputs : FloatTensor 1×98
labels: FloatTensor 1×98
hmmm, What it is caused by?