Attitude measurement system is an indispensable part of rocket simple guidance field. Based on magnetometer and MEMS gyroscope, traditional single-point attitude measuring method was studied and improved. Yaw angle solved by MEMS gyroscope was taken as input of three-axis magnetometer for measuring attitude angle. In view of the attitude measurement method, a three-axis magnetometer measuring system was designed and semi-physical simulation experiments were carried out on three-axis rotation platform. The results show that the improved method can satisfy missile attitude algorithm and the precision is improved.