Gate location and number setting are the key technology in injection molding. Flow direction and balanced flow of polymer depend on gate location and number whose optimization can promote product quality. Gate location and number of air switch side-axis were analyzed in injection flowing process with CAE software Moldflow. According the simulation results, the best gate location and number were set up. The study result is preparations for further injection system design and it provides evidence for mold optimization design. By utilizing the simulation results, the product quality is improved and the designing cycle is shortened.