The characteristics of current high orbit GPS (Global Positioning System) signal are of poor availability and low positioning accuracy. Positioning of high Earth orbit satellites using GPS/Beidou combined system is studied. The visibility of navigation satellites and the Geometric Dilution of Precision (GDOP) are analyzed. Through simulation and analyzing, it is verified that the GPS/Beidou combined system has better performance than that of single GPS system. On one hand, the GPS/Beidou combined system can receive more satellites' signal than single GPS system. On the other hand, GDOP of the GPS/Beidou combined system is smaller than that of single GPS system. At the same time, the use of high-precision atomic clock in the satellite receiver can realize positioning of three satellites, and reduce the technology requirements of receiver.