Cobalt base alloy is the most widely used hardfacing alloy because of its good high temperature resistance,corrosion resistance and wear resistance. In order to reduce the maintenance cost of operating units in nuclear power plant and improve the maximum utilization rate of equipment,the research on cobalt based hardfacing technology of valve element ASTM 216 WCB steel was carried out in the way of "replacement replaced by repair". In this paper,the types of hardfacing and the mechanism of wear resistance of cobalt base alloy are introduced, and the cobalt base alloy hardfacing procedure qualification of ASTM 216 WCB steel is described in detail. Through the non-destructive testing and physical and chemical testing of the hardfacing layer,a satisfactory hardfacing joint is obtained,which provides a strong technical basis for the establishment of the process instruction of the same material valve core cobalt base hardfacing for the overhaul of the unit,so as to ensure the quality of the valve core repair cobalt base hardfacing meets the requirements.