The azimuthal alignment scale of current azimuth alignment system based on sine wave magnetooptic modulation is narrow. The principle of azimuth alignment system and the mixed signal′s component from the modulator are analyzed, then an azimuth automatic alignment method in spatial wide-angle scale is present. The method of estimate azimuth is established based on the phase comprison between the modulation signal and the atternating current (AC) signal from modulator, and the independent measurement model of the initial light intensity signal is established according to the lower instrument′s initial setting place and running way, then the model of measuring glancing azimuth is presented based on the collected direct current (DC) signal from modulator in wide-angle scale, the lower instrument is controlled by the glancing azimuth signal and turned into the little-angle scale. The model of measuring azimuth accurately in little-angle scale is established based on the collected AC signal from modulator. Two models cooperate together to assurance the azimuth automatic alignment precision in wide-angle scale. The simulation results show that with the method, the system′s theoretic automatical alignment scale is -90°~90°, it can solve the current problem effectively.