Abstract: In order to understand the spectroscopic characteristics of chemical fibers in the terahertz region, the research trys to obtain the transmission spectra of three kinds of chemical fiber (Polyester, Kevlar 1414, Vinylon) by Tetahertz time-domain spectroscopy techniques and free-space electro-optic sampling method. And then the absorption coefficient and refractive index of the three fibers in the 0.2-1.0 terahertz region have been calculated. The experimental results indicate that the three fibers have the special response in terahertz spectral range, which could be used to detect the molecular structure and vibration of the sample. The results confirmed that the spectroscopy of different chemical fibers varies in the far-infrared region, terahertz spectrum can be used as complementary technology of the infrared spectrum to identify various chemical fibers.