Abstract: In order to solve the problem of steam oxidation of high-temperature heating surface of ultra-supercritical power plant boiler, research on the oxidation of domestic nickel-base alloy C-HRA-1 at 620~650 ℃/25 MPa and C-HRA-2 at 650 ℃/25 MPa in supercritical water is carried out. The oxidation kinetics, microstructure and phase composition of the oxide film are analyzed by precision electron balance, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). The oxygen isotope experiments at 600 ℃/25 MPa in supercritical water are also carried out to explore the oxidation mechanism of nickel base alloy C-HRA-1 in supercritical water. It is found that the main phase of C-HRA-1 and C-HRA-2 exposed to supercritical water is Cr₂O₃ and NiCr₂O₄, and the phase of NiO, CoO, MoO₃ and NiFe₂O₄ are also detected. The outward diffusion of cations in the alloy leads to the growth of oxide film. The domestic nickel-base alloy C-HRA-1 has excellent oxidation resistance in supercritical water.