Chlorpyrifos, a broad-spectrum and highly effective organophosphorus pesticide, is widely used in agriculture and other fields. However, environmental toxicology studies have found that chlorpyrifos can be directly applied to the soil, firmly binds to soil particles, hardly migrate or volatilize, and has low water solubility, which is likely to cause drug residues, thus affects the safety of agricultural and sideline products. Many countries have strict regulations on the residual amount of chlorpyrifos in agricultural products. Therefore, detecting the ecological risk of chlorpyrifos residues is a top priority. Surface-enhanced Raman spectroscopy has the advantages of fast, high efficiency and high sensitivity, and has become a hot technology in the spectroscopy research field. Density functional theory is widely used in theoretical simulation calculations and spectral analysis of molecular structure and properties. This paper, based on the surface-enhanced Raman spectroscopy technology and density functional theory, the theoretical study of chlorpyrifos Raman and surface-enhanced Raman spectroscopy is carried out. First, GaussView5.0 was used to configure the insecticide chlorpyrifos molecule and the molecular structure added to the silver cluster base. Second, the 6-31G basis set was used for the chlorpyrifos molecule, and the structure was optimized based on density functional theory, and then the Raman and surface-enhanced Raman spectra were calculated by Gaussian09 simulation. The Raman spectrum peak attributions were determined. Finally, the enhancement effect of silver clusters Ag₂ and Ag₃ on the Raman spectrum of chlorpyrifos was analysed from the frequency shift perspective, and the frequency shift was compared. The study found that the peak intensity of Raman spectrum at 326, 463, 741, 781, 1 068, 1 294, 1 435, and 1 602 cm^-1 wavenumber has a significant increase with the action of the silver clusters, and with the increase of the size of the silver cluster structure, the enhancement was more effective. Besides, the position of some characteristic peaks shifted and the frequency shift was related to the structure of silver cluster Correlatively. Raman spectrum of 463, 741 to 781 cm^-1 wavenumber produced a large frequency shift and the frequency shifts at other characteristic peak wavenumbers were all smaller than 20 cm^-1. The frequency shifts of the surface enhanced spectra of Ag₂ invasion with the chlorpyrifos molecule were in agreement with the shifts of Ag₃ invasion with the chlorpyrifos molecule. The results of this article provide a theoretical basis for applying surface-enhanced Raman spectroscopy for pesticide residue detection.