The corrosion behavior of N80 steel in an environment of supercritical CO₂ with a high H₂S content was investigated through corrosion tests, surface characterization, water chemistry analysis, and thermodynamic calculation. This investigation revealed the evolution mechanism of corrosion morphology and corrosion film. The results show that the corrosion morphology of N80 steel changes from general corrosion to localized corrosion with the extension of corrosion time. Initially, the predominant corrosion product is feathery FeS formed by solid-phase reactions, and the overall protective effect of the corrosion film is relatively poor, leading to severe general corrosion of N80 steel. After prolonged corrosion, the corrosion products transform into crystalline FeS and FeCO₃ formed by deposition reactions, and the corrosion film provides overall good protection, slowing down the corrosion of N80 steel. However, the uneven deposition of FeCO₃ and FeS induces localized corrosion of the substrate.