Abstract: For nuclear TP316LN stainless steel thick walled pipelines, 8 different batch numbers of stainless steel welding wires are used for narrow gap laser wire filling welding. By analyzing the mechanical properties and microstructure of the welded joint while maintaining consistent laser welding parameters, this study explores the influence of welding materials with different chemical compositions on the quality of the weld seam, and thus derives the basic principles and rules for selecting welding materials for laser wire filling welding.