In order to solve the problem of low theoretical muzzle velocity limit of conventional guns, the interior ballistic model of combustion light gas gun was established based on the combustion characteristics of hydrogen and oxygen. According to the principle of combustion light gas gun, the parameters affecting the interior ballistic performance of combustion light gas gun were obtained. Particle swarm optimization algorithm was used to optimize the launcher structure and interior ballistic parameters, and the Fluent coupling Chemkin method was used to further verify the optimization results of interior ballistic numerical simulation. The results show that the initial velocity of the optimized device decreases slightly, and the initial pressure and maximum chamber pressure of the combustion chamber decrease significantly, which has a high reference value in the early stage of combustion light gas gun research.