Abstract: Frequency-sweeping interferometry can be used to measure absolute distance and phase measurement plays an important part in it, because the precision of phase directly influences the precision of distance. The paper puts forward a new phase measurement method making use of Discrete Fourier Transform of reference signal and measurement signal. It does not start to sample until each signal crosses zero negatively. After the spectrum analysis, relative errors can be eliminated if zero-crossings can be tested before sampling signals. According to the theory, the paper has made simulations in LabVIEW, and the results show that the method has the advantages of high precision and good ability to overcome the noise. When the distance is 10m, the difference between the average of the measured phase and ideal value is 0.2, and relative uncertainty is 0.105%.