Abstract: The electron beam welding test of 20 mm thick TB18 titanium alloy plate was carried out, and the microstructure and mechanical properties of the TB18 base metal and the welded joint were compared.The results show that the average tensile strength of the base metal and the joint is 1330 MPa and 1344 MPa, respectively.The tensile strength of the joint is slightly higher than that of the base metal.The elongation of the base metal and the joint after fracture is 8.8% and 8.4%, respectively, and the plasticity of the joint is worse than that of the base metal.The tensile fracture of the base metal is composed of a lot of dimples, which is characterized by ductile fracture, while the tensile fracture morphology of the joint is mainly composed of dimples and cleavage planes, indicating that it is quasi-cleavage fracture.The average microhardness of the weld zone is highest, reaching 378 HV.And the microhardness of the base metal and heat affected zone is close, which is 364-368 HV.A large number of acicular secondary α phases are observed in the β grains of the three regions, but the length and width of the secondary α phase in the weld zone are smaller than that in the base metal.