In the process of rocket assembly, the segment docking is the key process of rocket launching quality. The traditional docking depends on “visual and call”, manual operation, assembly accuracy and stability are not high, and need to be adjusted repeatedly, labor intensity is large, assembly quality can not be guaranteed. Automatic docking has the advantages of high docking accuracy, high efficiency and good consistency. A method of automatic docking of rocket parts was introduced by using laser tracker to collect data, combining sliding mode control with synchronous control, and controlling the support frame car designed independently by workshop to adjust the attitude of the parts. The layout method of laser tracker and the principle of adjusting the attitude of mounting vehicle were introduced firstly, then the system was analyzed by using Lagrange method and the system control model was calculated. Finally, the feasibility of this method was proved by MATLAB simulation and practice.This method greatly improves assembly accuracy and assembly efficiency, and reduces labor intensity.