Abstract: The 7 mm thick TC4 titanium alloy plate was welded by vacuum electron beam welding. The microstructure of the welded joint was characterized by optical microscope, the microstructure composition of different areas was analyzed, the mechanical properties were studied by microhardness, tensile test, impact test and bending test, and the tensile and impact fracture morphology were observed by scanning electron microscope. The microstructure evolution and properties of the welded joint were studied. The results show that the welded joint is well formed by vacuum electron beam welding. The microstructure of TC4 titanium alloy base metal is composed of α phase and β phase, the microstructure of weld zone is the α′ phase transformed from the original β phase, that is, the acicular martensite is composed of thick columnar crystal structure, the heat-affected zone is composed of uniform and fine acicular martensite and the original α phase and β phase. The microhardness of weld zone is higher than that of heat-affected zone and base metal zone, and the microhardness decreases gradually from the top of weld to the root. The tensile strength of welded joint is higher than that of base metal. The impact specimen with V-notch in the weld zone has better toughness.