The terahertz (THz) and infrared spectra of solid pesticide difenoconazole are studied. The absorption spectra of difenoconazole are obtained at room temperature in the frequency range of 0.2 THz – 2.6 THz by using of terahertz time-domain spectroscopy (THz-TDS) and in the frequency range of 1.8 THz – 10 THz by the Fourier Transform Infrared Spectroscopy (FTIR). The experimental results show five significant absorption peaks in THz frequency range, respectively, 0.66 T, 0.80 T, 1.03 T, 1.31 T and 1.57 T, and those peaks corresponding to the abnormal dispersion. The spectral characteristics between 0.2 THz and 15 THz of difenoconazole are simulated by using of Gaussian03 software based on the single molecular model and the density functional theory (DFT). Both of simulation and experimental results fit well in the terahertz range. Moreover, the quantitative analysis of difenoconazole is studied based on the THz-TDS measurement. The absorption coefficient and refractive index spectra of difenoconazoles at different proportions doped with polyethylene (PE) are obtained. The partial least squares (PLS) model is built. It is possible to predict the concentration of difenoconazole in the mixtures by this method.