Gaussian software, Density Functional Theory(DFT) and Hartl-Fokker theory(HF) are selected to simulate the absorption spectra of glucose and fructose single molecules in the 0~3 THz band, and the results are compared with that in the reference literatures. The feasibility of using Gaussian software for single molecule absorption spectra calculation is verified, and the intramolecular vibration patterns corresponding to the absorption peaks at different locations are analyzed based on the results obtained by DFT.