Impersonal and normative determination of the moisture content is an important factor in monitoring the quality of the Pieces of Chinese Medicine. However, the conventional measurement method is time-consuming with low-efficiency, and cannot meet the fast, simple and in-situ requirements. In this work, the THz absorption spectra of Gastrodia elata BI with different moisture contents have been measured by Terahertz Time-Domain Spectroscopy(THz-TDS), and the obtained linear correlation between absorption coefficient and moisture content shows that THz-TDS method is expected to have potential applications for the quality inspection and determination of the moisture content in the Pieces of Chinese Medicine.