Corrosion behaviors of TP347H austenitic stainless steel were investigated in supercritical water at different temperatures. Results show that weight gains follow roughly parabolic kinetics except after 1800 h exposure at 650 °C. Some outer isolated Fe2O3 particles are interspersed on the inner nano-sized spinel scale at 380 °C. At 550 °C, the oxide layer with outer magnetite and inner spinel gradually increases and the (Fe,Cr)2O3 layer decreases with exposure time increasing. At 650 °C, the thick magnetite layer is firstly formed and then spalled associating with a chromia layer generated at the spinel/matrix interface, resulting in significant weight loss.