Abstract: With the development of technology, the method that acquires satellite ephemeris data from onboard GPS data directly becomes an important means of satellite orbit determination and an important research task. The satellite ephemeris obtained by GPS receiver is in an instantaneous state at a certain moment. The acquisition for continuous satellite ephemeris data needs further processing. The commonly used processing methods are based on geometry and dynamics. The calculation error of geometry would be great when the frequency of the instantaneous satellite ephemeris is low. Further more it is unable to conduct the extrapolating of the satellite orbit when only one group satellite ephemeris exists. Based on the analysis of Earth Resources Satellite orbit character, this paper proposed a novel reduced dynamic orbit determination which can reduce the calculation error of satellite ephemeris. The model breaks up satellite motion into simple harmonic motion in rectangular coordinate. The Paper make use of this determination to realize the orbit extrapolate algorithm. Finally, the result of our experiment indicates that the algorithm can reach high precision and reduce the complexity of calcLiiation process at the same time.