Abstract: “Beidou” Double-star positioning system is one kind of positioning system for local area （RDSS）. In this paper, the disadvantage of double-star navigation system is discussed and a new idea is put forward. The idea is to set an inactive regional navigation system made up of the barometer and the existing two working satellites and the third （spare satellite）. The algorithm expression for this navigation idea is presented. The simulation results show that this method for navigation is feasible and can fulfill the media-accuracy navigation positioning, so to offer a new way to develop a relatively simple satellite navigation system.