With the rising of both station distance and the speed gap betweencargo train and passenger train, there will be more cases of long section where thedifference of running time between cargo train and passenger train is bigger thanthe tracing interval in auto-block sections of double line.

Targeting the problems existing in drawing the passenger train flow diagram by hand, the essay develops the CAD system for passenger train flow diagram and respectively elaborated its three composites—the railway network, train flow lines and automatic drawing of diagram from the aspects of calculation method, idea and approaches.