Terahertz (THz) wave refers to electromagnetic radiation in the frequency interval from O.1 to 10 THz.THz time-domain spectroscopy (THz-TDS) is a powerful technique to study materials properties such as complex dielectric response and conductivity in the far-infrared spectral region, with the advantages of high signal-to-noise ratio, noncontact optical probe,and measuring the amplitude and phase of electric field simultaneously thus no requirement for Kramers-Kronig transformation.