Terahertz time-domain spectra technology can distinguish minor differences in structure and can be applied to physical testing and analysis.It provides a new experimental method for the identification of the organic chemical products and the study of spectrum more wide.In this paper,the optical property and spectroscopy of methanol,anti-freeze liquid and brake fluid are studied based on the terahertz time-domain spectra in the terahertz range.At room temperature,the time-domain spectra and the absorption spectrum in the 0.2~2.5 THz region of these samples are obtained in the environment full of nitrogen.Methanol,anti-freeze liquid and brake fluid have significant different absorption spectra in this wave band.The absorption peaks of methanol are located at 0.72 THz and 0.35 THz and the main absorption peaks of anti-freeze liquid and brake fluid are located at 0.62 THz.Experiment results show that whether methanol exists in anti-freeze liquid or brake fluid can be detected using THz-TDS terahertz time-domain spectra technology and then its quality can be judged.