Abstract: The microstructure and properties of pure titanium TA2 and 14 MnMoVN steel joint after vacuum diffusion welding were studied by adding copper foil transition layer. The microstructure of the joint was analyzed by metallographic microscope. The interface area was observed by scanning electron microscope, and the distribution of the main elements was scanned. The composition of the interface phase was analyzed by the energy spectrum analysis and X ray diffraction analysis. The mechanical properties of the joint was examined by the tensile test. The results show that the titanium steel vacuum diffusion welding with copper transition layer can achieve a good bonding effect. The interfacial bonding is good, and the interface can be divided into diffusion transition zone and copper titanium binding zone. The diffusion transition zone is formed when titanium diffuses into copper, and a small amount of iron diffuses into copper. The titanium binding zone is the area where copper diffuses into the titanium, and a large amount of Cu-Ti intermetallic compounds are formed in this region. The tensile strength of the joint can reach 299 MPa and the fracture is located in the Cu-Ti junction region.