Abstract: In order to make the arrival time of up and down direction passenger trains join mutually in drawing up of a passenger train diagram to shorten the change and ride time of passengers in a transfer station, the congruence theory was applied to investigate the time interrelation for two passenger trains from up and down directions in a big station in the way.A method for calculating reasonable departure time was proposed.With this method, the departure time of the second train reaching at the transfer station is calculated based on the departure time of the first train reaching at the transfer station, and so a feasible solution is found out.Furthermore, the problem to mutually joining of arrive time of more passenger trains can be solved with the proposed method by transforming it into that of two passenger trains.