Abstract: The laser welding technology of 16 mm thick TC4 titanium alloy medium plate was studied. The influence of auxiliary gas blowing on the laser penetration welding was studied firstly, and based on the above study, the single pass penetration welding with two sides forming of 16 mm thick TC4 plate was realized. The metallographic structure of the laser welded joint was analyzed, and the tensile, microhardness, impact and bending properties of the joint were tested. The results show that the welded zone is mainly composed of needle α', martensite α, a small amount of needle α and β phases, coarse high temperature β phase boundary can also be observed, the heat affected zone is mainly composed of needle α', block α, martensite α and a small amount of β phase, in partial area the needle α' and β phases present network characteristics. The average tensile strength of the joint is 965 MPa, the tensile fractures are ductile rupture. The average hardness of the material is the minimum, the average hardness between the heat affected zone and the weld zone is similar, and a typical "soft + hard + soft" sandwich hardness distribution structure is formed. The absorbing work between the weld zone and the heat affected zone is similar, the average impact absorbing work of the base material is the minimum, and the bending property of the welded joint is good.