<p>The NiCoCrAl_0.3Fe high-entropy alloy is an excellent high-temperature structural material, exhibiting good phase stability and mechanical properties during service in high-temperature environments. However, there is limited research on the oxidation mechanism of NiCoCrAl_0.3Fe high-entropy alloy in high-temperature environments. In this study, NiCoCrAl_0.3Fe high-entropy alloy with a single-phase FCC structure was prepared using vacuum arc melting technology. The oxidation mechanism of NiCoCrAl_0.3Fe high-entropy alloy at 1100&#xa0;°C was investigated during the initial stage of oxidation, and the results indicate that the Al element in the high-entropy alloy preferentially undergoes oxidation, followed by the Cr element. The Al element, which oxidizes preferentially, forms granular Al₂O₃ due to its content in the alloy being below the critical concentration (16.13%). Cr ions within the alloy diffuse outward along the interface between Al₂O₃ particles and the high-entropy alloy, forming a continuous Cr₂O₃ layer on the surface of Al₂O₃. During the oxidation process, Al₂O₃ particles transform into elongated Al₂O₃ structures through inward diffusion into the alloy. Subsequently, aggregation and lateral growth occur, leading to the transformation of Al₂O₃ into a continuous layer when the volume fraction of Al₂O₃ within the inner oxidation layer reaches 19.78%. This transformation hinders the outward diffusion of metal ions and the inward diffusion of external oxygen ions, further enhancing the high-temperature oxidation resistance of NiCoCrAl_0.3Fe high-entropy alloy.</p> Graphical Abstract <p></p>