The material of VVER-1000 MCL（main coolant line in nuclear power plant connects with reactor pressure vessel,steam generator and reactor coolant pump,thus constituting the primary loop pressure boundary） is the composite pipe with large thickness and dissimilar metal. Welding procedure of VVER-1000 MCL is complex,and the welding shrinkage is difficult to control. In this article,starting from the selection of welding material,formulation of welding parameters and other aspects,an effective and reasonable welding procedure is analyzed scientifically and formulated to ensure the welding quality.