Solved by Igo312 in post #8 
              
              
                @ptrblck thank you for your help 
I know where I am wrong. Here’s my second stage to feed input 
cls, offset = self.model([proposal, fm], stage='two') 
proposal is the ROI whose shape is [N, 5], the 1th dim is the batch index. e.g. The batch size is 4, the range of index is [0,1,2,3]. And fm is the …