Abstract: Based on the virtual simulation technique in the assembly process design, an application system of the virtual simulation of the spacecraft assembly process is built. The process and the method for the establishment of the spacecraft virtual assembly and integration environment are discussed under the context of the assembly process design in the Lunar Exploration Project II-CE-3. The applications of the virtual simulation in many assembly processes are illustrated, including the assembly process flow design, the implementation plan, the MGSE(mechanical ground support equipment) optimal design, and the ergonomics analysis. The project application results indicate that the virtual simulation technique can optimize the process of the spacecraft assembly and integration design, and enhance the efficiency of the process design, and increase the rationality of the MGES, and reduce the dependency on the personal experience during the process design.