Abstract: The conventional design method of gear transmission has some disadvantages, such as complicated calculation process, relying on engineering experience and need to check repeatedly. Therefore, this paper takes the two-stage spur gear transmission as the research object, and establishes the optimization model with the minimum volume of the gear transmission mechanism as the optimization objective. The optimization model of gear transmission was optimized by improved particle swarm optimization. The results show that compared with the conventional gear transmission design method, the volume of the gear transmission system optimized by the improved particle swarm optimization algorithm is significantly reduced, and the optimization effect is good.