The maximum assembling for some period on nested routing platforms of urban rail transit line were calculated by trend analysis method. Based on influencing factors of maximum assembling on platform, relative hypotheses were given. Platforms were divided to eight types by relations between platform and routing train. Interaction of passenger, train and platform, assembling change process, and calculation frames of maximum assembling on different type platforms carried out to be maximum assembling were concluded by trend analysis method. The numerical example application revealed that trend analysis method to calculate maximum assembling on nested routing platforms is feasible, and the final results by trend analysis method are more accurate than by one of codes for design of metro.