Di-n-butyl phthalate ( DBP ) is one kind of Phthalate esters ( PEs ) widely employed as plasticizers in the production of polymeric materials. PEs are dialkyl and alkyl aryl esters of 1,2-Benzenedi-carboxylic acid, which comprise a wide group of compounds. Since these compounds are not linked to the polymeric matrix, they can migrate from their original containers to the surrounding environment, resulting in ubiquitous environmental pollutants. The infrared vibration spectra of isolated DBP was assigned according to DFT calculations by Gaussesview 5.0 software with First Principles. The method of B3LYP of the density functional theory ( DFT ) at 6-31G* level has been used to calculate its geometrical parameters and convergence criteria. Compared with the Fourier transform infrared spectrum of DBP in 400~4 000 cm-1 band, the characteristic absorption peaks of the simulation spectrum were broadly in agreement, and the position of the peaks were almost corresponding to each other. Considering the influence of the experimental conditions and temperature, theoretical calculations were in good agreement with experimental data. According to the linear fitting of the peak position of the experimental spectra with respect to the theoretical spectra, the correlation degree is more than 99%. This research provides a theoretical basis to the detection and analysis of DBP.