An integral valve seat is an essential component in ultra-super critical (USC) thermal power plants. Onsite remanufacturing of the valve-seat sealing face is a major focus of thermal power plant manufacturing. In this paper, a laser cladding Stellite 6 Co-based alloy repair study was carried out for the commonly used SA182 F91 heat resistant steel for nuclear valves. A series of cladding thick-size repair samples were prepared by changing the process parameters, and the metallographic observation, hardness testing, three-point bending testing, and impact testing at room temperature were performed. The cladding layers consisted of a face-centered-cubic γ-Co solid solution with epitaxial growth solidification characteristics. The hardness, bending strength, and impact energy of the repaired samples were 450‒500 HV, 1246‒1582 MPa, and 40‒60 J, respectively. Bonding strength between the cladding layer and substrate was very high. The gas pore and bad bonding often exist in a cladding layer. The selection of cladding process parameters should follow the principles of low power density and high reliability.