In order to achieve rapid capture of low-rail IoT signals under the conditions of high dynamic and low signal-to-noise ratio, a partial matching filter-fast Fourier transform (PMF-FFT)improvement algorithm for rapid capture of low-rail IoT signals is proposed. First of all, the ephemeris information is used to predict the Doppler frequency bias and narrow the frequency domain search range; then, the scallop loss of PMF-FFT algorithm is overcomed by zero padding and windowing. Finally, the frequency domain differential incohere accumulation is used to improve the output gain under low signal-to-noise ratio. The simulation analysis shows that the proposed algorithm can improve the detection probability of low-orbit iot signal when the signal-to-noise ratio is -25~-15 dB, and the search range is reduced from 15~35 kHz to 24.8~25.2 kHz.