Abstract: The earth background radiation and its suppression technologies for satellite-ground laser communication system were studied. Firstly, a theoretical formula of the power of entrance pupil caused by earth background radiation at different orbits was derived, and the concept of inherent stray radiation was put forward and theoretically deduced. Furthermore, theoretical calculations of earth background radiation for a typical terminal were accomplished, and baffle system designs of different forms were given. Finally, optical simulation software LightTools was used to simulate the stray radiation of the terminal with different forms of baffle system at different orbits, and then the curves of stray radiation affected by orbit altitude and the form of baffle system were obtained and analyzed. This article provides a theoretical foundation of earth background radiation for the satellite-ground laser communication and a simulation basis for baffle system of the laser communication terminal on the satellite.