Plasma arc welding experiments were performed on 4mm nickel-based superalloy Inconel625 thin plates, and the microstructure of each part of the welded joint under three different welding heat inputs, the mechanical properties of the joint, the fracture morphology, and the high-temperature corrosion behavior of the base metal and the weld were compared.The results show that the structure of Inconel625 plasma welded joint is composed of the austenite equiaxed crystal of the base material and the cell crystal near the weld fusion line and the dendritic crystal in the center of the weld.There is a large amount of carbide and a small amount of Laves phase precipitation at the weld, making the mechanical properties of the welded joint reduced, the toughness of the weld becomes a weak link in the joint.In the welding heat input of 10.175KJ/cm when the mechanical properties of the joint is optimal, the tensile strength of 765.3MPa and the parent material of 785.4MPa equivalent, elongation of 31.9% compared to 42.8% of the parent material has decreased.Specimens fracture by ductile fracture occurring at the weld seam.Base metal and weld metal at 750°C after 24h molten salt corrosion corrosion products are basically the same: the outer layer of granular NiO and Cr2O3 and NiCr2O4 corrosion layer.