The problem of satellite ground stations planning is of fundamental significance for optical satellite networks, especially in terms of network capacity and blocking ratio. In this paper, a new metric, i.e., uniformity, is introduced in optical satellite networks, and a satellite ground station planning based on the gravity model (GSP-GM) algorithm is proposed. Simulation results show that the GSP-GM algorithm can increase the number of ground-satellite links effectively and reduce about 6% blocking rate.