Abstract: There are many factors which influence the selection of spacestation orbit,such as mission requirements,radiation environment,meteoroid/debris environment,configuration of space station,vehiclecapability,launch window and logistics demands of space station.The resupply delivery system performance for space station generally tendsto favor lower orbit altitude,but the orbit maintenance requires higher alti-tude.This paper describes the effects of resupply,orbit maintenance and solaractivity on the orbit altitude,and presents the optimum operation altitudesof space station.It's also calculated two numeral examples for mannedspacecraft delivery system and shuttle delivery system.The main conclusion is that the optimum orbit altitude of space station isnot constant.It varies with the solar activity,delivery system and trafficlevels.During period of high solar activity,the orbit altitude should be adjustedupward.As the traffic levels to space station are increased,the optimumoperation altitude should be lower.