Abstract: Welding tests on 2. 5 mm-thick Ti6321 titanium alloy plate and 5083 aluminum alloy plate were carried out by electron beam welding, and the mechanical properties and microstructures of the welded joint were investigated. The results show that the microstructure of the titanium side and its heat affected zone is mainly martensite structure composed of α' phase and originalα phase, the aluminum alloy side mainly consists of coarse columnar grain structure, while a small amount of Ti-Al intermetallic compound precipitates near the weld line; the tensile strength of the welded joint is about 219 MPa, and the fracture position is mainly on the aluminum side of weld line, and partly on the Ti-Al intermetallic compound.