Abstract: The butt test of Incoloy 825 nickel base superalloy in air cooler tube box was studied by electron beam welding. The microstructure of electron beam welded joints was analyzed by observing the structure of welded joints, and the mechanical properties of electron beam welded joints were analyzed with tensile properties and impact toughness tests. The results show that good weld joint of lncoloy 825 alloy can be obtained by electron beam welding. The weld zone is composed of large equiaxed grains and a few columnar crystals. There is no obvious element loss in the we4ld area. The hardness of weld and heat affected zone reaches the hardness value of base metal. The tensile strength of the weld joint reaches 600 MPa, which is close to the tensile strength of the base metal, and the fracture form of the joint is ductile fracture. The impact value in the weld and heat affected zone is higher than that of the base metal, in which the impact energy in the weld joint reaches 262 J, and the impact fracture morphology is ductile fracture.