The accurate measurement of the rolling attitude of the ammunition is the premise of precise guidance. In the common attitude measurement schemes that combining satellite navigation and magnetometer, large-scale maneuvering of the ammunition can cause the large angle measurement error. In order to solve the above problems, a new combined attitude measurement scheme of magnetometer and satellite navigation based on BP neural network calibration is proposed. For the same type of missile, the control command, ballistic speed, historical attitude angle and other parameters are used to estimate the sideslip angle information of the missile body in real time. Simultaneously, the declination angle of the missile body calculated by the satellite navigation system is calibrated online. Finally, the rolling attitude of the projectile is measured by fusing the measurement information of the magnetometer, and the accurate rolling attitude estimation is provided through the fitting and filtering scheme for the real-time control of the ballistic trajectory. The numerical simulation results show that for the same type of ammunition system, the sideslip angle information error of the projectile that estimated by the trained BP neural network is within 5% of the full scale. The roll attitude angle accuracy obtained by the fitting and filtering after the combination of the satellite positioning and navigation system and the magnetometer is within ±1°, which greatly improves the roll angle measurement accuracy of the ammunition during maneuvering.