Abstract: Diagnostic shield module is the core component of international thermonuclear experimental reactor（ITER）diagnostic port plug, and its water circuit network lids are welded by automatic Arc TIG welding, which has capability to weld7 mm thickness in a single pass and no spatter under the backside of the weld. Its welding current is higher compared to conventional TIG welding. In order to study the effect of high current on the microstructure and mechanical properties of Arc TIG welded joints, which can provide reliable welding parameters for production of products, taking 7 mm thick 316L（N）-IG（IG is an abbreviation for ITER Grade） austenitic stainless steel forgings as research object, the Arc TIG welding was carried out. The results show that the microstructure of the weld zone is single austenitic phase, and no cracks are found. The ultimate tensile strength of the welded joints at room and high temperature are greater than minimum design requirements of 316L（N）-IG forging. There is no visible crack on the surface of the welds of the specimens after bending to 180°. The impact absorption energy of the welding area and heat affected zone at room temperature are greater than 60 J, the fracture surface shows a ductile fracture mode with fine dimples observed by SEM analysis, which indicates that the welded joint has good impact toughness.