In order to study the effect of the amount of direct defocus on the weld quality、microstructure and mechanical property of TA2 industrial titanium plate welded by vacuum laser. A vacuum chamber and a high-power disc laser are used to weld with different defocus at a vacuum degree of 4.0×10-1 Pa. The results show that：the amount of positive defocus can effectively complete the welding of plate. In the vacuum environment, with the increase of defocus, the forming quality of the weld surface is improved and the weld width is increased. However, the increase of defocus will lead to the dispersion of spot energy. Therefore, when the defocus reaches +4 mm, the weld width reaches the maximum and then begins to decline. The grain size and form of the weld and heat-affected zone are different under different defocusing amount, and the grain size decreases with the increase of defocusing amount. Through the research on the effect of positive defocus on vacuum welding of TA2 industrial titanium plate. When the defocus is 0 mm, the microhardness of the weld is increased 1-2 times. When the defocus is +4 mm and +8 mm, the microhardness of the weld has no obvious change. The tensile force and tensile strength of the weld reached the maximum value of 57 759 N and 292 N/mm, respectively, when the defocus amount of +8 mm was used. The conclusion is drawn: using vacuum welding of TA2 industrial titanium plate with +4 mm to +8 mm defocus can get better comprehensive performance of weld seam. This is of great significance to its application in the field of shipbuilding.