Abstract: The microstructure and properties of TC4 titanium alloy welded joint by hot-wire tungsten inert gas arc welding (TIG) were studied. Metallographic microscope was used to observe the microstructure characteristics of the welded joints, and the microhardness and mechanical properties of the joints were also measured. The results show that there is no welding defect inside the hot-wire TIG welded joint of titanium alloy, and the weld performance is excellent; The weld is of a typical casting structure consisting of thick columnar grains and a small number of equiaxed grains, and elongated needle like α′ phase can be seen inside the grains; Coarse equiaxed grains are formed in the heat affected zone, which mainly consist of fine needle like α phase and residual β phase; The average tensile strength of the welded joints is 924 MPa, equivalent to that of the base metal; The impact energy of welding line by hot-wire TIG is obviously higher than that of the base metal, and the maximum reaches 66 J, more than 1.5 times higher than that of base metal; The cold bending angle of the welding line meets the requirement of the index.