<p>The high-temperature corrosion behaviors of an as-rolled Fe–17.4Cr–12.4Ni–2.63Mo–1.57Mn–0.044C (in&#xa0;wt.%) austenitic stainless steel in nuclear-grade helium environments containing with 10, 100 and 1000 magnification impurity tolerance concentrations at 550&#xa0;°C were investigated and compared. Based on the quantitative relationship between mass gain and corrosion time, the high-temperature corrosion kinetics curves of the alloy in different helium environments were determined. The results demonstrated that for different samples, their mass gains exhibited a parabolic increase over the corrosion time. Raman spectroscopy and GIXRD analyses revealed that the high-temperature corrosion mechanisms of different samples are similar and the formed surface oxide layers were primarily composed of Fe₂O₃, Cr₂O₃, Fe₃O₄ and NiFe₂O₄. Under the equivalent corrosion damage and mass gain conditions in helium containing with 10, 100 and 1000 magnification impurity tolerance concentrations, the corresponding corrosion time required to achieve a mass gain of 0.5&#xa0;mg/cm² were determined to be 200, 600 and 1000&#xa0;h, respectively. Based on the principle of same damage mechanism and equal damage degree, an acceleration testing method was proposed and the corresponding empirical formulas were established for evaluating the long-term high-temperature corrosion extent of austenitic stainless steels in nuclear-grade helium environments.</p>