链路持续时间是影响卫星量子密钥分发量子比特率的重要参数。文章分析了影响星－地单光子和纠缠光子量子密钥分发链路持续时间的若干因素，并且进行了数值仿真研究。结果表明，随着轨道高度的增加或者地面最小通信仰角的减小，单光子和纠缠光子链路的持续时间有较大的改善；单光子链路时地面站同卫星星下点轨迹间的距离和纠缠光子链路时两地面站之间的距离也均是影响链路持续时间的重要参数；纠缠光子链路持续时间的影响因素较单光子链路更为复杂，其最终决定于卫星星下点轨迹同两地面站之间的位置关系。

Link duration is one of the most important parameters which influence the quantum bit rate of the satellite-ground quantum key distribution. The factors that may influence the link duration are analyzed, and the simulation shows that with the increasing of the orbital altitude and the decreasing of the minimum elevation angle, the link duration is improved greatly; meanwhile,the distance between ground track of satellite and ground station is very important to the link duration of single photons link, so is the distance between two ground stations to entangled photons link; in the end ,the link duration of entangled photons link is more complex than single photons link for its influencing factors,it is eventually determined by the relation of the ground track of satellite and the location of two ground stations.