Single-satellite positioning system can provide support for the rapid deployment of target positioning, under the circumstance of access denied such as planetary detection, war damage and other navigation constellations, however, the larger orbit determination error will bring larger positioning error. Therefore, this paper presents a single satellite positioning method based on factor graph co-location assistance. Firstly, it constructs the positioning hyperboloid by using the pseudo range difference of different sets of satellites at different time, which provides continuous positioning for the positioning target. And then establishes the synergy factor graph to assist the positioning result of the single satellite positioning system by using the high-precision ranging information between multiple positioning targets, so as to improve the positioning accuracy. The method proposed in this paper is compared with the existing Doppler single star positioning method and radial acceleration single star positioning method from three aspects of satellite orbit determination error, ranging error and positioning error, and the simulation results show that the localization error of the proposed method is only 10% of the other two methods.