Abstract: An aluminized coating was prepared for P92 steel using low-temperature pack cementation process at service temperatures, while a study was carried out on the oxidation behavior of P92 steel and the aluminized coating in saturated steam at 650℃ by the way of oxidation weight gain, scanning electron microscope and X-ray diffraction analysis. Results show that P92 steel has poor steam oxidation resistance and its oxidation kinetics follow the parabolic law in the first 350 h; the double-layered oxide scales consist of Fe₃O₄+Fe₂O₃ outer loose layer and FeCr₂O₄ inner layer formed during exposure, and the outer loose layer peels off severely after oxidation for 700 h. As for aluminized P92, however, its steam oxidation resistance could be improved significantly due to the formation of a protective Al₂O₃ film on the surface. The major degradation of aluminized coating is not the consumption of aluminum to grow Al₂O₃ due to its slow growing-rate, but the inward diffusion of aluminum into the substrate to form AIN phase and the outward diffusion of Fe into the coating to form Fe₃Al, thus decreasing the concentration gradient of aluminum from the top surface to the base metal.