The precise measurement of the attitude angle of guided projectiles is crucial for the precise control and accurate strike of guided projectiles. Regarding the issue of how to accurately measure the attitude information of the projectiles during trajectory correction for guided projectiles, a scheme of attitude measurement combining magnetometer and gyroscope is put forward. The initial attitude of the projectiles is resolved by comparing the output information of the on-board magnetometer with the standard geomagnetic field information. Considering that the high overload and high impact during the launch of the projectiles may lead to abnormal gyroscope signals, to enhance the adaptability of the system, the Kalman filtering algorithm and the interactive multiple model (IMM) algorithm are combined to achieve data fusion of the output information of the magnetometer and the gyroscope, thereby realizing the subsequent update of the projectiles" attitude. Moreover, flight experiments of the projectiles were carried out to verify the combined attitude measurement scheme. The results indicate that this method can accurately obtain the attitude of the projectiles.