Abstract: Co alloy coating was deposited on 304 stainless steel by TIG(Tungsten Inert Gas Arc Welding) cladding technology. Compared to 304 stainless steel used as material for hydroturbines flow passage components, Co alloy coating was evaluated by cavitation erosion test. Microstructure and cavitation erosion resistance of coating were observed and measured by OM, X-ray diffraction, SEM and microhardness test. The results show that the coating has high microhardness and good cavitation erosion resistance. The improvement in corrosion resistance of the coating is due to the occurrence of stress induced martensite phase transformation, strengthen effects of boride precipitated phase and intermetallic compounds of Co.