Abstract: Double-Star positioning system is one kind of regional satellite positioning system built up in China, it’s aim is to provide more accurate position information for the user, but it’s shortcoming is that the real-time positioning is dufficulty to get. It is one new concept to use the Double-Star positioning system to measure the attitude. This paper introduces one kind of the basic principles of attitude determination with Double-Star positioning system on the basis of the satellite simulator and gives the mathematic model of the attitude measurement. Thus the shortcoming mentioned above can be overcome. When the position and attitude information of Double-Star positioning system and strap-down inertial system are integrated, the state and measurement functions are built up, the simulation is made under specific orbit. The simulation results show that the system’s accuracy can be improved effectively.