In such environments as forestsindoor rooms and high-altitude orbits with weak signalsthe satellite navigation receiver can not use the traditional Frequency-Locked Loop (FLL) to track the Doppler frequency of received signal normally.To solve this probleman improved algorithm of FLL based on maximum likelihood estimation is proposed.In this algorithmthe maximum likelihood estimation module is inserted before the mixer of the traditional FLL.The proposed algorithm is formulated in detail.Based on the structure of traditional FLLan implementation scheme is also proposed to enhance its performance.Simulation results show that:Compared with the traditional FLLthe improved algorithm has a great improvement on the performance of frequency tracking.