Abstract: In order to implement the parametric modeling of railway line structure, the construction process of a customized subassembly parameterized model was studied based on Autodesk Civil 3D subassembly composer(SAC). Using the subassembly composer's visual design process and parameter-driven graphical interaction method, a parametric model of single-line ballasted track subassembly, tunnel subassembly and multi-level slope subassembly was constructed for different cross-section forms. The parameterized subassembly was fused with the threedimensional terrain surface model, and the precise calculation of the engineering quantity of the design subassembly was implmented in the three-dimensional visual environment. The subassembly created by SAC has the advantages of convenient change of design parameters, rapid modeling, strong interaction, visual and intuitive. It is an effective method to model railway BIM application subassembly.