Abstract: Urban rail transit adopts fixed long formation marshalling for train operation. It is difficult to balance the constraints among operation capacity, operation cost and operation service level during normal peak period. Based on analysis of flexible marshalling requirements, operation status of lines adopting flexible marshalling is introduced. Taking Shenzhen Metro Line 9 as example, specific flexible marshalling scheme is introduced, as well as function requirements and implementation. Economic benefits from using three-section formation train operation for normal peak hour are analyzed. Assigning trains of different formation at different hour of the day depending on the urban rail transit general operation brings about not only technical feasibility, but also economic benefits.