High main steam parameters can effectively improve the generation efficiency of coal-fired power stations. However, once the temperature and pressure of water vapor exceed the critical point, it shows strong oxidation. Austenitic steel HR3C is widely used in superheaters and reheaters of power stations. It is very important to evaluate the high temperature oxidation property of HR3C in supercritical water. Oxidation experiments of austenitic stainless steel HR3C in supercritical water environments at 605, 640 ℃ and 26 MPa are performed to investigate the oxidation resistance of HR3C steel. The supercritical water oxidation experimental system can withstand the maximum temperature and pressure of 700 ℃ and 27 MPa. The samples are suspended in the constant temperature section of the reactor. The experiment adopts the method of interrupt experiment at interrupt time points of 300, 500, 800, 1 500 and 2 000 h respectively. The sample is weighed before and after the experiment. It provides a data support for the research on the damage mechanism of boiler tube material in coal-fired power stations. In order to explore the mechanism of oxide film growth, the oxidation experiment of austenitic steel HR3C in supercritical water containing H218O is further carried out in a static autoclave. For the oxygen isotope labeling experiment, it is carried out in supercritical water (H216O) for 100 h in a static reactor, followed by oxygen-containing isotope supercritical water (H216O+H218O). Based on the distribution of oxygen isotopes, it can reveal the diffusion path of oxygen and the growth process of the oxide film. The oxidation kinetics, surface oxide morphology and structure, elemental composition and phase composition are identified by electronic balance, scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer, X-ray diffraction, X-ray photoelectron spectrometer and secondary ion mass spectrometer. The oxidation kinetics of austenitic steel HR3C follows near the parabolic law at 605 ℃ and deviates from the parabolic law at 640 ℃. It indicates that the oxidation process is controlled by ion diffusion. The oxide formed on HR3C is mainly Fe3O4/spinel, Fe2O3, Cr2O3 and MnO. The oxide films consist of a Fe-rich outer layer and a Cr-rich inner layer. The oxygen isotope 18O located at the outer oxide film is detected. Scale spallation from HR3C is observed after 2 000 hours at 640 ℃. The oxidation rate and spalling tendency of HR3C increase with the increase of temperature, the outward diffusion of metal ions in the initial oxidation stage leads to the growth of the oxide film, and the diffusion of metal ions and oxygen ions lead to the formation of the double-layer oxide film in the long-term oxidation process. The high chromium-rich oxide content formed on the surface of HR3C due to the high metal chromium content. It can effectively prevent the outward diffusion of metal cations and the inward diffusion of oxygen. Thus, HR3C shows high oxidation resistance. The approximate service environment and the use of the isotope tracer method can effectively evaluate the oxidation resistance of HR3C stainless steel. The results of this paper can provide a data support for the oxidation resistance evaluation of austenitic steel HR3C.