Research conclusions ： Based on the analyses of survey and design flows of new railway lines at different grades, CAD for railway line are presented and researches are done on the key technologies of establishing digital ground model， interaction of the graph with the data, the interactions of track plane section, track longitudinal section and track lateral section, interaction design of railway II line, track scheme management and real 3D visuals of design. The application results show the CAD based on these technologies can be generalized and applied in the construction design.