In the long distance laser communication system, it is necessary to control the dispersion angle of laser beam in real time in order to suppress the influence of complicated atmospheric channel environment. However, the traditional optical zoom system has low precision in adjusting the laser beam scatter angle, which requires mechanical movement of the distance between the lens groups, resulting in poor flexibility and real-time performance. In this paper, a method of controlling laser beam scatter angle using liquid crystal on spatial light modulator (LC-SLM) is proposed. LC-SLM was used to simulate the zoom lens, and the phase gray images with different focal lengths were generated by computer and imported into LC-SLM. The applied voltage of LC-SLM was controlled by the gray information of different phase gray images to realize the function of the zoom lens. Then, the control system of beam scattering angle was composed of the zoom lens and the matching lens with known focal length. The distance between the zoom lens and the matching lens was constant, and the beam scattering angle was controlled by changing the focal length of the zoom lens. The results show that the error between the variation value and the theoretical value is within 5%, and the RMSE of the beam divergence angle is 0.017 5. The root mean square error of beam divergence angle is reduced by 22% compared with the traditional method of controlling beam divergence angle by mechanically moving the distance between lens groups, which provides an important technical support for dynamic adjustment of laser parameters.