Abstract: Oxidation experiments of P92 steel were conducted in supercritical water at 650 ℃ and 30 MPa with an oxygen content of 100 μg/L. The phase, morphology, structure, and elemental distribution of the oxide film were characterized using Raman spectroscopy and scanning electron microscopy (SEM), and the oxidation behavior and mechanisms of P92 steel were investigated. The results show that the growth of the outer layer, inner layer, and total thickness of the oxide film approximately followed a parabolic law over time, while the thickness of the inner oxide layer remained essentially unchanged. With increasing oxidation time, the central pores of the surface Fe₃O₄ particles gradually healed, and the particle size increased. Subsequently, a loose and porous Fe₂O₃ layer with slight Cr enrichment formed on the surface. The inner oxide layer consisted of fine oxide particles, preferential oxidation channels along the interface, and residual matrix. As oxidation time increased, the preferential oxidation channels eventually evolved into discontinuous Cr-rich layers, leading to localized thinning of the oxide layer. The thickness of the oxide film became increasingly influenced by the microstructure. Ni elements diffused and enriched in the inner layer.