By using the Particle Swarm Optimization (PSO), this paper, optimizes main parameters of missile in the view of the problems in mass restricting the overall parameter design of inter air to air missile. Firstly, according to the flight characteristics of air to air missile at different stages, a numerical integration method is used to settle the mass of air to air missile based on the existing model of boost stage and cruise phase. Secondly, taking the minimal takeoff mass as the objective function, the paper optimizes load mass, relation coefficient of projectile body, structure coefficient of engine, wing loading, boost stage and cruise phase specific impulse by Particle Swarm Optimization (PSO) algorithm. In the end, through dissertation comparison of the optimized velocity curve and deceleration time curve with the original, the advantages and the reliability of the model are verified. The results show that the mass of missile can be reduced by optimizing, and the flight performance remains unchanged generally. This is for designing missile reference only.