Electron beam welding of 30CrMnSi alloy steel and TC4 titanium alloy was realized by Cu/V interlayer.Microstructure and mechanical properties of the joint were investigated. The results show that by adding Cu/V transition layer metal, the direct mixing of Ti-Fe elements and the brittle intermetallic compounds can be avoided. Characteristic phases of different components and properties are distributed in different areas of the weld. The weld near the steel side is a mixture of Fe-rich phase and Cu-rich phase. The weld near the titanium side forms Ti-V solid solution and also forms a small amount of Ti-Cu intermetallic compounds. The maximum tensile strength of the joint is 418 MPa,and the joint fails at the interface between the weld and 30CrMnSi base metal.