Abstract: The single and twice (weld in the same process at the first weld) welding tests of 21 mm thick TC18 titanium alloy plate were carried out by electron beam welding. The effects of welding time on the structure, tensile properties and hardness of the joint were studied. The results show that the two kinds of welded joints were well formed and had no obvious defects. Compared with those of the single welding joint, the α′ phase content and the grain size in the heat affected zone of the twice welding joint increased. The tensile strength of the welding joints was higher than that of the base metal, and that of the twice welding joint was higher, but the percentage elongation after fracture decreased. The fracture modes of the both two joints were ductile fracture. The average microhardness in the weld zone of the single and twice welding joints was 380, 395 HV, respectively, which was higher than that in the base metal, and that of the heat affected zone was 360, 350 HV, respectively. Increasing welding time improved the hardness of the weld zone and reduced that of the heat affected zone.