Abstract: With an experimental analyzing method,which combined the alloying principle with application feature,a Co-223A alloy powder has been developed for plasma arc spray-welding.The plasma arc spray-weld metal can opeate at 750℃ for a long time and has high resistance to heat,wear and erosion. Its deposited metal has a low rate of dilution, about HRC 40 hardness at roon temperature and a high cracking resistance.While it is apray-welded to the seal surface of exhaust valves in high speed disel engines,the service life of the exhaust valve can be increased by 4 to 6 times.