Abstract: A method for analyzing THz time-domain spectroscopy based on Hilbert-Huang transform(HHT) was presented. THz pulse of vapor can be decomposed into a number of signals with single frequency, and using Hilbert transform to those components can acquire the instantaneous frequency. The final presentation of those results is an energy-frequency-time distribution, designated as the HHT spectrum, which is compared with the time-frequency distribution based on wavelet transform. The results indicate that the method can improve the temporal resolution and frequency resolution, and it has the feature of localization analysis and adaptive selection. The HHT based THz-TDS is feasible in researching the mechanism on interaction of THz with materials by time-domain and frequency-domain.