Abstract: At present,space-borne GPS receivers have gradually evolved into a standard tracking system for low Earth orbiting (LEO) satellites.In order to produce high accuracy onboard navigation solutions continuously,an extended Kalman filtering model of real-time orbit determination with space-borne GPS measurements is firstly derived based on the dynamic model compensation method,and relevant software named SATODS is developed subsequently.Then a simulative test was carried out using broadcast ephemerides and space-borne GPS dual frequency pseudo-range data from CHAMP satellite with SATODS.The results compared with JPL RSO demonstrate that real-time orbital accuracy about 1.0 m for satellite position and 1.2 mm/s for velocity (3 d RMS) is feasible with dual-frequency code measurements.In addition,it is hardly subjected to data quality of GPS observation such as the number of GPS satellite and the value of PDOP,and so on.