In this paper, the capillary substrate is prepared by Adsorption of silver nanoparticles on the inner wall. By using surface-enhanced Raman spectroscopy (SERS) to detect pesticide dimethoate in Rapeseed oil, under neutral conditions pesticide dimethoate concentration was found to be 200 mg/kg, and under acid conditions pesticide dimethoate concentration was found to be 0.1 mg/kg. It is close to the national safety standard of maximum pesticide residue(0.05 mg/kg) in vegetable oils. The experimental results showed that the surface-enhanced Raman spectroscopy technology can be used as an effective method for detecting the residues of Dimethoate pesticides in Rapeseed oil.