The absorption spectra of Ⅰ and Ⅲ polymorphs of chlorpropamide were measured with terahertz time-domain spectroscopy (THz-TDS) technique, FT-IR and FT-Raman at room temperature. The results showed that there were distinct differences of Ⅰ and Ⅲ polymorphs of chlorpropamide in those spectra. The IR spectra of two polymorphs of chlorpropamide had showed differences both in the frequencies of the vibrational bands and in the relative band intensities. The obvious differences in Raman spectra of polymorphs of chlorpropamide were that the characteristic peaks of Ⅲ-form were more than Ⅰ-form in 100~1 800 cm-1 region. Absorption peaks observing in the terahertz spectra ofⅠ-form were at 0.90, 1.09 and 1.29 THz and Ⅲ-form were at 0.92, 1.11, 1.23 and 1.63 THz. The maximum difference between Ⅰ-form and Ⅲ-form was that the strong peak appeared at 1.63 THz of Ⅲ-form. The characteristic absorption bands of two polymorphs of chlorpropamide were assigned based on the simulation results of DFT calculation. The simulation result is in accordance with the experiment. From simulation results, it is found that the vibration modes of Ⅰ-form and Ⅲ-form were similar in IR and Raman spectra, but there were more differences in terahertz spectra. The study can provide experimental and theoretical references for the application of FT-IR , FT-Raman and THz-TDS spectra techniques to detect pharmaceutical polymorphs.