In this paper, the terahertz time-domain spectroscopy system (THz-TDS) was used to obtain the terahertz absorption spectra of two isomers of sugars D-(+)-glucose and D-(-)-fructose, and found that D-(+)-glucose and D-(-)-fructose have obvious differences in the terahertz absorption peak positions in the 0.3~1.72 THz frequency band. D-(+)-glucose and D-(-)-fructose can be distinguished by the two absorption peak positions of 1.41 and 1.66 THz. In order to study the formation mechanism of the absorption peak of D-(+)-glucose terahertz spectrum, the unimolecule configuration of D-(+)-glucose was first constructed, and the B3LYP functional in density functional theory was used to complete the D- (+)-Glucose unimolecule configuration optimization and frequency calculation. It is found that the quantum chemistry calculation results based on the D-(+)-glucose unimolecule configuration are quite different from the experimental spectrum. Then the D-(+)-glucose crystal structure configuration was constructed, and the generalized gradient was used to approximate the PBE functional in GGA. The structure optimization and frequency calculation of the D-(+)-glucose crystal structure configuration were completed using CASTEP software. It is found that the quantum chemistry calculation results based on the D-(+)-glucose crystal structure configuration are more consistent with the experimental spectrum. In the quantum chemistry calculation of the D-(+)-glucose crystal structure configuration, the hydrogen bond between the molecules and the effect of van der Waals forces are considered comprehensively, indicating that the absorption peak of D-(+)-glucose at 1.41 THz is formed as a molecule Weak interaction between. Secondly, the vibration mode of D-(+)-glucose at 1.41 THz absorption peak was identified by Materials Studio 2017 software, and it was found that the absorption peak of D-(+)-glucose at 1.41 THz was mainly the interaction between molecules, which further explained The absorption peak of D-(+)-glucose at 1.41 THz is mainly the weak interaction between molecules. Based on the quantum chemistry calculation results, use Multiwfn software to perform RDG calculation on D-(+)-glucose crystal structure, and use VMD software to determine the type, position and intensity of weak interaction between molecules in D-(+)-glucose crystal structure Conduct visualization research. The research results show that terahertz time-domain spectroscopy technology can keenly perceive the subtle changes in the structure of carbohydrates and correctly identify its isomers.