Research conclusions :(1)Urban rail transit system should be designed based on the connection intension of central city，suburban and exurban，with different levels of rail transit configuration. Developing the suburban railway can improve the rail transit system of large cities. ( 2)The railway which has spare capacity in Beijing railway terminal can be a part of the urban rail transit system，and undertakes the function of urban rail transit.(3)There are three patterns on developing the suburban railway:extending the urban rail transit，taking advantage of existing railway by appropriate transformation to have the function of operating suburban passenger train，newly building suburban railway. ( 4)This research has reference meaning for the construction of large urban rail transit system and carrying out research on undertaking urban rail transit function by taking advantage of lines in existing railway terminal.