Methimazole (MMI) monolayers on the silver surface were studied by electrochemical impedance spectroscopy (EIS), electrochemical polarization measurement, and surface-enhanced Raman scattering (SERS) spectroscopy. The EIS mechanism of the silver surface with MMI monolayers was fitted with the mode of LR(QR)(QR), and the electrochemical polarization experimental results showed a high inhibitive efficiency around 82.6%. SERS results indicated that the MMI molecule with a tilted orientation anchored at the silver surface via S-6, N-2-, and N-5 atoms, resulting in a strong interaction between the MMI molecule and the surface. In situ electrochemical SERS observation suggested that the molecule experienced a transition state of the adsorption because of the electrochemical hydrogen evolution reaction occurred about -0.1 V vs SCE.