damaoooo:

and it hangs in clothModel = nn.parallel.DistributedDataParallel(clothModel)


You mean DDP hangs at constructor? Can you attach the process to gdb and check the trace to see line is causing the hang?
Have you set CUDA_VISIBLE_DEVICES or pass in device_ids arg properly for DDP? Each DDP process should exclusively work on one GPU.

I wonder is there something wrong with my  clothModel?

Given the trace, I assume you are using the launch script. With that, DDP should be constructed in the following way:
clothModel = DistributedDataParallel(clothModel, device_ids=[arg.local_rank], output_device=arg.local_rank)