The corrosion behaviors of ferritic-martensitic steel P92, austenitic stainless steel type 316L and nickel-based alloy 690 have been investigated in supercritical water (SCW) at 600℃ and 23 MPa. After exposed to SCW for 625 h, the weight gain of alloy 690, 316L and P92 are 0.001 02 g/(m
2·h), 0.060 6 g/(m
2·h) and 0.101 27g/(m
2·h), respectively. SEM observation shows that a three-layer oxide film is formed on P92, a single-layer oxide film is formed on 316L and a very thin oxide film with some pitting is formed on alloy 690.