A 50 mm thick TC4-DT alloy plate was welded using electron beam. Ultimate tensile tests of base metal, weld metal and the whole joint were carried out to collect the tensile property data. Moreover, microstructure and fracture morphology after tensile tests were observed to study the effect of electron beam welding on tensile properties of TC4-DT alloy. The results indicate that both the base metal and weld metal exhibit high strength and weak strain hardening ability. Electron beam welding makes the weld strength and strain hardening ability increase, while the plasticity and ductility decrease. Base metal is the weakest part of the whole joint, and the fracture occurs on the base metal away from the weld metal during the tensile tests of the joints. In addition, fractography of both the weld metal and base metal is found to be dimple, which means that the fracture feature of both the base and weld metal is ductile. The tensile property difference between the base metal and weld metal is related to the microstructure change of weld metal after welding. The increase of strength and decrease of plasticity and ductility for weld metal is mostly dependent on the formation of coarse β columnar grain and martensite in the weld metal due to the very fast cooling speed during electron beam welding