Abstract: To study the corrosion of alloy materials for high-temperature components in supercritical carbon dioxide (S-CO₂) Brayton cycle power generation system, and in order to further study the corrosion resistance of different types of alloys, the corrosion behavior of nickel-based alloy GH 3128 and martensitic alloy AISI 616 at 550℃ and 20MPa in S-CO₂ environment for long-term (up to 900h) is investigated. The effect of stress loading on the corrosion behavior of the alloy is studied by using a four-point stress device. The microscopic morphology, oxide phase and oxide film thickness of the samples after the experiment are analyzed by SEM (Scanning electron microscope), XRD (X-ray Diffraction), and XPS (X-ray photoelectron spectroscopy). The experimental results show that the nickel-based alloy GH 3128 forms a single-layer Cr₂O₃ oxide film, while the martensitic alloy AISI 616 forms a double-layer oxide film structure, in which the outer layer is mainly Fe₃O₄, and the inner layer is Fe-rich and Cr-rich oxide. With the increase of corrosion time, the thickness of both oxide films increases, but the final thickness of GH 3128 is much smaller than that of AISI 616, and the amount of carburization is also small, while AISI 616 has obvious carburization. Stress loading can accelerate the corrosion rate of the alloy, increase the thickness of its oxide film, promote carburization, and change the structure of its corrosion products. Moreover, the effect of stress loading on AISI 616 is much higher than that of GH 3128. The results show that the resistance of nickel-based alloy GH 3128 to oxidation, carburizing and stress corrosion is higher than that of martensitic alloy AISI 616. Therefore, GH 3128 is recommended for S-CO₂ Bryton cycle power generation systems at 550℃ and 20MPa.