The purpose of carrier tracking is to make the duplicated carrier signal consistent with the received signal, so as to strip the carrier from the satellite signal. Therefore, the tracking accuracy of the carrier tracking loop determines the final positioning accuracy to a large extent. Considering the Doppler frequency shift caused by the high dynamic characteristics of satellites, the tracking loop requires good dynamic performance while also having good tracking accuracy. Therefore, the loop needs to simultaneously utilize the characteristics of Frequency-Locked Loop (FLL) with good dynamic adaptability to the signal and Phase-Locked Loop (PLL) with good tracking accuracy to the signal. The theory of FLL and PLL is analyzed, and based on this, adopts a method of using a second-order FLL assisted by a third-order PLL based on threshold adjustment. Finally, the algorithm is simulated by Matlab. The results show that the tracking loop can track the signal faster and has better tracking accuracy.