Abstract: Due to the disadvantages of a traditional GPS receiver in the environment of weak signal are that slow convergence rate and serious tracking error, a GPS signal tracking algorithm is proposed, in which the coherent integration of I/Q branch is considered as measurement of Unscented Kalman Filter (UKF). The filter model of the baseband signal processing is constructed and tracking loop is closed by UKF. Then the signal parameters of GPS tracking loop can be accurately estimated. Moreover, the anti-jamming capability and tracking ability of receiver are improved in the presence of weak signals. Simulation results demonstrate that the tracking ability and convergence rate of proposed algorithm outperform traditional method in the case of different Carrier to Noise ratio (C/N).