Abstract: A frequency tracking discrete Fourier transform (DFT) algorithm based on frequency sweep for analyzing the swept sine test signal is proposed. The fundamental frequency is identified based on the zero crossing and the least squares techniques. The discrete time signal is truncated at integer periods according to the fundamental frequency, to minimize the effect of the frequency spectrum leakage in the analysis of the harmonics, and the spectrum of the truncated signal is calculated by the DFT to obtain the harmonic amplitude of the sample signal. This method is used to analyze the frequency spectrum of the sinusoidal vibration test data of a spacecraft, and the accuracy is compared with that of other time-frequency analysis methods. It is shown that the proposed method has a good adaptability and can be used to reduce the error of the frequency analysis.