Removal of X-ray-induced carbon contamination on beamline optics was studied using radio-frequency plasma with an argon/hydrogen (Ar/H2) mixture.Experiments demonstrated that the carbon removal rate with Ar/ H2 plasma was higher than that with pure hydrogen or argon.The possible mechanism for this enhanced removal was discussed.The key working parameters for Ar/H2 plasma removal were determined,including the optimal vacuum pressure,gas mixing ratio,and source power.The optimal process was performed on a carbon-coated multilayer,and the reflectivity was recovered.