On the basis of research on the assembly process of CA6140-type lathe spindle system, the assembly relationship of its components was ascertained. Three-dimensional (3D) components storehouse of the system was established with CAD software UG6.0. On that basis, dynamic simulation software of assembly process and power transmission process of the system was developed. Running the software can reproduce assembly, disassembly and power transmission process. The software can not only be used in the analysis and transformation of old products, but also can be used replacing prototypes in developing of new products.