Abstract: In order to explore the stability of special vehicle body under launch load, the finite element modeling and simulation method based on HyperMesh-LS-DYNA was used. Taking a special vehicle as the research object, the suspension and other related flexible components were constructed in the vehicle numerical simulation model, and the stability of the car body under the launch load was analyzed. It was found that the launch load was not uniformly dispersed to each supporting structure. In addition, the contact pressure between the tire and the ground corresponding to the launch base and g-h axes was larger, and the swing amplitude of the launch tube was larger. Based on the above results, two optimization schemes were proposed to adjust the stiffness and damping coefficient of the branch structure and increase the additional supporting structure, in order to reduce the contact pressure between the vehicle and the ground and the longitudinal swing amplitude of the car body, and the simulation verification was carried out. The results show that the number and position of auxiliary supports have a great influence on the stability of the car body, and the more close to the base and the more the number is, the better the stability of the car body is, in which a pair of additional supporting legs is added between the axis of g and h, and the base contact force is reduced by 16%. A pair of additional supporting legs are added between the axis of b and c, and are added between the axis of g and h at the same time, the base contact pressure is reduced by 20%, and the swing range of the launcher is reduced by 12. 1%.