Because the return error of angle instrument’s limit switch is large, control accuracy of function and fire area is not high. According to the practical problem, working principle of angle instrument’s limit switch is studied, mathematical model of working process is established,and parameter optimization design is carried out by complex method. Major factors affecting error are obtained by causality diagram based on PDCA, and measures are taken to solve them one by one. After verification, it is real- ized that the return error of cam limit switch is reduced to under 0. 5°, control accuracy of function and fire area is improved, and the expected goal is reached.