The application of the wavelet-transform to terahertz time-domain spectroscopy (THz-TDS) is described. Using wavelet-transform to analyze the time-domain signals passing through water vapor measured by time-domain spectroscopy, we got the absorption spectra of water vapor in the frequency range from 0.5 to 2.5THz, which agree well with the results reported in the literature. Moreover, wavelet-transform in THz-TDS opens up a new way for the analysis of the time-domain properties of absorption spectra of water vapor.