A Plasma Surface Interaction （PSI） experiment on China Low Activation Martensitic （CLAM） steel was done to check if CLAM steel could be used as a Plasma Facing Material （PFM）. A specimen with a diameter of 45 mm was exposed to 897 shots of deuterium plasmas with a total duration of 712 sec at a minor radius of 30 cm in HT-7 tokamak. During the exposure experiment, no observable influence was found on plasma performance. After exposure, the surface of the specimen seemed as smooth as before but with some colour change at the margin of the specimen. Even though some micro-damage, such as dense blisters, melting, splashing, depositions, and dust, was found on local surfaces with Scanning Electron Microscopic （SEM） observation. The reflectivity of the specimen decreased only slightly. All of these shows CLAM steel has good stability and irradiation resistance. With further optimization, it could possibly be used as the first mirror material for plasma diagnostics in tokamaks.
