A low complexity asynchronous multiuser detection algorithm for on board LEO satellite receiver, which can resist strong multiuser interference and large doppler frequency drift is introduced. After chip match filter, base band signal was sampled at chip rate and used as observe signal. Then Kalman filter was used to separate multi-user signal. Doppler frequency drift and timing error were considered in state transform equations. The proposed algorithm can resist as high as 35dB near-far effect, and are senseless to frequency and timing error.