The pump cover of nuclear high temperature liquid metal pump is made of 316 austenitic stainless steel for nitrogen control.The welded joints have the characteristics of large thickness,large diameter,large welding filling and high mechanical properties. It is not only difficult to ensure the welding quality and mechanical properties of joints but also low welding efficiency and high labor intensity of welders by other methods. The welding efficiency is improved,the welding quality is guaranteed and the welded joints with excellent comprehensive mechanical properties are obtained by using a special developed submerged arc welding wire of φ2.4 mm and matching flux,combining with narrow gap groove and reasonable welding parameters. It provides an effective reference for the manufacture of similar products.