One scheme of the space solar power station (SSPS) is based on the laser beam for energy transfer from space to the earth. In order to demonstrate the feasibility of laser energy transfer, the analysis of the propagation process of laser beam in atmosphere is needed. Modeling and simulating processes are conducted. We analyze the effect of atmosphere towards laser beam at different heights, simulate the intensity profile of laser beam, and discuss the change of atmospheric temperature and refractive index at different heights. The results show that in order to reduce influence of atmosphere and avoid energy loss, the laser power density should remain within a certain range. Increasing the laser beam size can reduce the laser power density at a certain power level.