The sealing surface of nuclear valve with 1Crl8Ni9Ti base metal was clad with Co base alloy powder by using a 5 kW transverse flow CO2 laser. The dilution of laser cladding layer diluted by base metal composition was determined, the microstructure and dilution of laser cladding layer was compared with that of plasma spurt welding layer on the same kind of test piece. The result shows that under conditions of fine metallurgical combining with the base metal the dilution of laser cladding layer is much lower than that of plasma spurt welding layer, and that the laser cladding layer has fine micr...