Abstract: Objective Effective connection between N4 pure nickel and 321 stainless steel (321SS) is one of the important means to solve structural problems of hydraulic rocket thrust chamber. Methods Electron beam welding process of N4 pure nickel and 321 stainless steel (321SS) is tested. Typical microstructure and phase composition of welded joints are analyzed by means of metallographic microscope, scanning electron microscope and X-ray diffractometer, and microhardness distribution and tensile properties of welded joints are tested. Results N4/321SS electron beam welded joints are well formed. Due to the huge thermal conductivity difference between the two base metals, welded joints are not fused. Weld zone of welded joints is mainly solidification substructure which is composed of cellular dendrites and cellular crystals, and solidification mode is all austenitic solidification. Grains in heat affected zone near fusion line on the N4 pure nickel side are significantly coarsened, while fine grains are formed in heat affected zone far away from fusion line due to recrystallization. Microhardness of weld zone of N4/321SS welded joints is between the two base metals, and microhardness of heat affected zone on the pure nickel side is the lowest. N4/321SS welded joints are fractured in heat affected zone on the pure nickel side. Tensile strength of welded joints reach 96.5% that of pure nickel base metal, and fracture mode is ductile. Conclusion Weldability of electron beam welding of N4/321SS is good and weld microstructure is full austenite.