Diffusion bonding has been gaining increasing attention in the manufacturing of precise and intricate structural components in aerospace and other industries. The bonding temperature is a critical factor that affects the performance of the parts produced by diffusion bonding. This study explores the impact of hot-pressing temperature on the microstructure, mechanical properties, and fracture mechanism of TC4 titanium alloy joints formed through diffusion bonding. Samples were prepared using a hot-pressing technique. The findings reveal that dynamic recrystallization occurs at the diffusion bonding interface during the process. At lower temperatures, this recrystallization results in the formation of a fine α-phase at the interface. As the hot-pressing temperature increases, the α-phase progressively coarsens. Notably, there is a substantial disparity between the size of the α-phase formed through dynamic recrystallization at the interface and that in the nondiffusion zone of the base material, leading to a crystallographic mismatch. This mismatch substantially reduces the properties at the diffusion interface and consequently leads to fracture in the diffusion-bonded joints within the bonding zone after hot pressing. In the post-heat treatment, the diffusion zone consists of primary α (α_p) phase, needle-like secondary α (α_s) phase, and β phase. Elevating the bonding temperature gradually increases the size of the α phase, thereby improving the crystallographic match at the bonding interface and facilitating interface migration. After the heat treatment at 970 ^oC, the tensile strength and elongation of the 950 ^oC diffusion-bonded TC4 Alloy joints were measured at 998.7 MPa and 17.5%, respectively, achieving the performance levels of the alloy before diffusion bonding.