The technique of transmitting spatial azimuthal information between equipments without mechanical connection is important in spaceflight, military and other fields. The precision of the traditional azimuth measurement system is low, and the measurement scale is narrow, so the traditional azimuth measurement system cannot meet the requirement of transmitting the azimuth in high precision and wide scale. The modulation wave of the traditional method is transformed, the square wave magneto-optic modulation is introduced into the azimuth measurement system, and the azimuth measurement model based on square magneto-optic modulation is established. The model of modulated signal is presented according to Malus law, and its characteristics are analyzed. The equation between azimuth and modulated signal is established according to their relationship, and the variation trend of modulated signal is used to delete the equation′s extraneous roots. The phase comparison of modulation signal and modulated signal is used to widen the azimuth measurement scale. At last the azimuth measurement model based on square wave magneto-optic modulation is acquired, realizing the transmission of azimuth between equipments without mechanical connection. Simulation results show that compared with the traditional method, the theoretical measurement precision of the new method is higher, and the measurement scale is wider, which provides a reference to measure azimuth in high precision and wide scale.