Abstract: In satellite formation flight, the measurement and determination of independent relative orbit is one of the most important techniques of formation flight. The traditional techniques of using star sensor, radar and GPS(global positioning system) signal to determine relative orbit are considered. Relative orbit determination which is based on pseudo satellite technique is considered. Pseudo satellite technique means that carrier generators and receivers are assembled onboard, and are used to measure the distance between satellites. In these projects, differential carrier-phase GPS sensors are used, and nonlinear equations are solved by optimization methods. These methods of measurement adapt different situation. On the base of measurement results from previous three projects, using the concept of relative orbit elements, precision of orbit determination is improved by Kalman filter. Emulation calculations indicate that the request of keeping formation can be satisfied, and a part of results is presented.