The Dynamics Analysis & Simulation of the Rocket Sled were done based on Multibody System Dynamics and Finite Element Analysis Theory. The most difficult work in the analysis was establishing the boundary conditions of the rocket sled. The paper made this kind of attempt. Then the relevant post processing figures and data were obtained, thereby providing the designer and manufacturer with detailed and reliable data. The conclusion is the simulation method is more effective than those before and the boundary conditions is correct and acceptable.