Abstract: This paper studied the determination of autonomous orbits of HY2A and ZY3 missions using on-board GPS data. A simulative on-board processing of real-time orbit determination was carried out using the space-borne GPS dual frequency pseudo-range and phase measurements with the auto-developed software SATODS. The test demonstrates that, based on pseudo-rang data, the position and velocity error (3D RMS) of orbit results are up to 1.3 m and 1.2 mm/s respectively, but with phase data, they are reduced to 38cm and 0.36 mm/s for HY2A mission, where the radial accuracy is about 10 cm, and decreased to 54 cm and 0.54 mm/s for ZY3 mission. These contributions can be used for certain real-time service of continued low-earth orbiters (LEO) for earth observations.