Traditional identification method and modern identification method are the main methods in the field of Chinese herbal medicine detection. Although the traditional identification method is widely used in research because of its advantages such as simplicity and low cost, the accuracy of identification depends to some extent on whether the operator has rich knowledge and experience in medicinal materials. With the development of spectral analysis technology, modern identification methods based on spectral analysis technology have gradually entered people’s field of vision. Theoretical and a large number of experimental studies have shown that the intramolecular vibration mode of the Chinese herbal metabolites and the low-frequency vibration of the lattice occur in the terahertz band, which can be used to identify the components contained in the Chinese herbal medicine. Glycyrrhizic acid is the main component in licorice. Glycyrrhizic acid was selected as the research object. The terahertz absorption spectrum of glycyrrhizic acid was simulated by a quantum chemical calculation method. The terahertz absorption characteristic of glycyrrhizic acid matched the molecular vibration mode. This work is deeply understood. The interaction of various groups within the glycyrrhizic acid molecule and the formation mechanism of the spectrum are necessary. In order to ensure the reliability of the simulation results, it is necessary to establish the initial configuration of the glycyrrhizic acid molecule, select the appropriate calculation method for structural optimization and frequency calculation, and finally obtain the terahertz absorption spectrum data of glycyrrhizic acid. Through the Gaussian09 semi-empirical theory PM3 algorithm, the characteristic absorption peaks of the glycyrrhizic acid terahertz are located at 0.87, 1.17, 1.56 and 2.76 THz, respectively. The characteristic peak at 1.56 THz is exactly the same as the experimental results in the reference literature, verifying the reliability of the calculation results. Since each glycyrrhizic acid molecule contains 120 atoms, the system is so large that it cannot exhibit its complete structure when it is analyzed by vibration mode. Therefore, the planar structure of glycyrrhizic acid molecules is used instead of the three-dimensional structure to carry out the vibration of the terahertz characteristic absorption peak. Turn analysis. The analysis shows that the terahertz characteristic absorption peak of glycyrrhizic acid molecule is related to the oxygen-containing functional group and the ring-like vibration of the carbon ring, but is mainly formed by twisting of the oxygen-containing functional group in the glycyrrhizic acid molecule.