Abstract: Research on 20 steel has been conducted due to its excellent weldability in the nuclear industry.Full-position automatic welding technology can greatly improve the installation efficiency of nuclear power pipelines.However,the conventional full-position automatic welding technology will have quality problems such as depression and limit its further application.Thus,this study focused on the 20 steel,utilizing an automated welding process with melting pad to achieve welding.The research results indicated that the pad was placed in the position of the filling metal before welding,and during the initial welding process,the pad fused completely with the weld root and became a part of the weld seam.The study on the automated welding process and joint performance analysis of the 20 steel showed that the use of melting pad could effectively solve the problem of depression in the automatic welding of the pipe in an upward welding position and meet the requirements of nuclear power construction standards for the welded joint.