Diffusion bonding was carried out between titanium alloy (TC4) and oxygen free copper (OFC) in vacuum and good transition joints were formed. The microstructure and elements’ composition were characterized by XRD, SEM and EDX. The tensile strength of the welding joint was measured. The results show that with the welding temperature increasing, the tensile strength of the welding joint increased first and then decreased. Thus the optimum welding parameters were 800 °C , 5 MPa and 30 min. The interdiffused layer with gradually varied element composition was formed at the interface of TC4/OFC welding joint. Cu3Ti2, Cu4Ti3, CuTi and Cu4Ti were formed at the interface of titanium and copper. The fracture morphology indicates that the fracture mainly took place at the weak bond of TC4/OFC interface. And the pores at the joints and species and thickness of the intermetallics played an important role in the bond strength of TC4/OFC.