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　beta　columnar　grain　and　martensite　in　the　weld　metal　due　to　the　very　fast　cooling　speed　during　electron　beam　welding.