Abstract: In order to improve the coupling degree between urban rail transit transportation capacity and traffic volume, and to solve the problem of low train load factor during non peak hours, a flexible train formation mode is proposed. Based on the temporal uneven distribution of urban rail transit line passenger flow, a demand analysis is conducted on the flexible train formation mode. Through the analysis of signaling system and vehicle network transmission operation, the process of train disintegration and formation is studied, and the operation time of train disintegration and formation is obtained to be 84.2 s and 103.2 s respectively. Considering the morphological distribution of passenger flow throughout the day, a transition scheme for the urban rail transit train flexible formation mode is proposed. It is suggested to use small formation trains departing from depot for the period before morning peak hours, and to use train disintegration on the main line during the peak to non peak transition period. Targeting the different train operation scenarios during the peak to non peak transition period, taking the ′3 car formation A type vehicle + 3 car formation A type vehicle′ flexible formation train as an example, train passing capacity is analyzed by drawing station operation diagrams, which verifies that train disintegration operation on the main line could meet the requirements of train passing capacity during transition period under flexible train formation mode. Research is also conducted on the problem of coupled train middle non through for evacuation under the above mode and the problem of train rescue under extreme conditions, and corresponding solutions are proposed. The flexible train formation mode of urban rail transit can improve the matching degree of traffic organization and passenger flow temporal distribution.