The satellite-to-ground optical link is greatly influenced by atmosphere, the intensity of laser beam would attenuate up to tens of dB after transmitting through the clouds, which induces that the laser communication system should work under visually cloud-free condition. So optical link availability must be considered when the optical communication system is designed and the ground station location is selected. Based on ten years’ statistics data of cloud cover in different cities across our country, the usability of ground station is calculated by using a simple model. The result can provide suggestions for selecting satellite-to-ground optical communication ground station location.