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.