Terahertz (THz) wave has strong resonance absorption with the hydrogen bond of polar substances. The bigger the molecular polarity, the stronger the absorption. Based on this characteristic, monohydric alcohol liquids from methanol to 1-butanolwere have been detected by terahertz time-domain spectroscopy (THz-TDS) within the spectral range of 0.2-1.0 THz. The relationship between the polarity of monohydric alcohol and their terahertz spectra are analyzed, which proves that the terahertz spectroscopy of monohydric alcohol molecules is mainly determined by the polarity, which can be quantitatively calculated. These results conclude that terahertz spectroscopy can realize the effective and fast identification of the polarity of chemical solution, which can provide a reference for liquid polarity detection.