Due to influence on missile separation parameter caused by elastic deformation and hook collision in multi-body dynamic simulation of missile ejection device, a missile ejection launcher with hook device and rigid-flexible coupled multi-body dynamic model was proposed. Based on elastic deformation theory and multi-body dynamics theory, the rigid-flexible coupling dynamic model of ejection device was established using PATRAN and ADAMS, and sensitivity of the model parameters was analyzed. The simulation results show that elastic deformation of structure, mass center and missile quality and air supplying pressure of actuating cylinder have influences on missile separation attitude.