Aimed at the influence of initial disturbance in the process of sloping launching of vehicular missile, disturbance mathematics model is established from theory point of view, and three-dimensional model software and finite element analysis method are used to build vehicular missile rigid-flexible coupling dynamic model. Through simulated analysis, influence curve of missile movement parameters from instability of engine power, shock of gas flow are gained. According to the results, the instability of engine power is the main source of initial disturbance. The model sensitively reflects launching process of missile and the results provide theoretical references for decreasing initial disturbance and increasing launching accuracy.