Abstract: The oxidation behavior of Inconel alloy 740H in dynamic pure steam at 750 ℃ was studied with high temperature oxidation test. The results show that the mass gain of Inconel alloy 740H during oxidation followed a parabolic law approximately. The oxide products grew coarse with the increase of oxidation time. The scale morphology was significantly different from those after oxidation in dry air. But non obvious cracks and spallation were observed. After oxidation for 100 h, the protective Cr2O3 film formed on the surface. The thickness of oxide film increased with time increasing. After oxidation for 1 000 h, the oxide film was composed of Cr2O3 and a small amount of (Mn, Ni)Cr2O4 spinel. Beneath the oxide scale, chromium depletion region was found and a small amount of inner oxides identified as Al2O3 and TiO2 were observed.