The self-assembled (SA) film of 2-mercapto-5-methyl-1,3,4-thiadiazole on the cathodic (McMT) was prepared on iron surface. The film was characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The results showed that McMT molecules formed a stable film on iron surface, which effectively protected iron from corrosion. The protection efficiency of the McMT self-assembled film was then calculated. The highest protection efficiency of McMT on the iron surface was ∼95.0%. Quantum chemical calculations and molecular simulations were further applied to reveal the adsorption structure and explain the experimental results.