Abstract: In this paper, TC4 titanium alloy bars were employed to study the effect of forging deformation on the microstructure and mechanical properties of the diffusion bonding interface. The results showed that the TC4 titanium alloy interface was metallurgically bonded by diffusion bonding process at 950 ℃ and 140 MPa for 4 h. The strength of the diffusion bonded sample was 95% higher than that of the base metal, and the elongation was 7%. The brittle fracture occurred in the diffusion zone. After high-temperature forging, the diffusion bonding interface of the TC4 titanium alloy completely disappeared. The microstructure consisted of an equiaxed α phase, a secondary α phase, and a small amount of β phase. With increasing forging deformation, the size of the equiaxed α phase decreased, the volume fraction of the secondary α phase and the alloy strength increased. When the deformation was 40%, the content of the equiaxed α phase and secondary α phase reached the best matching degree. The tensile strength reached 950 MPa, the elongation reached 17.5%, and the fracture mode of the alloy transformed into ductile fracture.