The roll attitude angle of projectile and rockets could be measured in real time using geomagnetic field vector information with long-term stability characteristics. In this paper, the theoretical model of the missile borne geomagnetic angle measuring device was established, and the preliminary simulation analysis was carried out. The theoretical model could be used as the reference for the hardware design, device debugging and calibration and DSP algorithm design. The simulation results showed that there were obvious differences in the characteristics of the geomagnetic digital signals for different operational environments, and the installation error of the structure had a great influence on the angle measurement accuracy of the missile borne geomagnetic angle measuring device.