In this work, the methanol molecule spectrum and the methanol-Ag1 surface-enhanced Raman spectrum were simulated. And a SERS substrate of silver NPs on copper surface was prepared by substitution reaction to detect the concentration of methanol dissolved in transformer oil. Based on this SERS substrate, we effectively detected the Raman signal of methanol in 1 mL/L methanol-oil solution, and the wavenumber of this Raman signal is at 1032 cm-1. Our study provides reference for further study on in situ detection and quantitative analysis of methanol in transformer oil.