Aiming at the signal-capturing difficulties faced by ground terminals when receiving low-orbit navigation signals due to the large Doppler frequency caused by the fast satellite motion speed, an improved capturing algorithm of PMF-FFT is proposed. Based on the detailed analysis of the mathematical model and the improvement method of PMF-FFT, adding window functions and complementary zeros to the PMF module and the FFT module respectively can significantly reduce the output gain attenuation and scallop loss of the capture system, and combine with the high-precision frequency interpolation estimation algorithm to estimate the frequency of the captured Doppler frequency. Simulation results show that the improved algorithm can capture the 100 kHz large Doppler frequency bias signal, and the frequency estimation accuracy is improved by one order of magnitude compared with the direct estimation.