The Dynamics Analysis & Simulation of the Rocket Sled were done based on the Multibody System Dynamics and Finite Element Analysis Theory. The most difficult work in the analysis is how to establish the boundary conditions of the rocket sled. This paper makes this kind of attempt. Then the relevant postprocessing 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 are acceptable.