This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS (time-domain spectroscopy). As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500 μm GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening.