Abstract: In order to solve the problems of melting depth and melting width reduction, and unstable welding process caused by severe scattering of electron beam in low vacuum and local vacuum electron beam welding. The variation of electron beam and weld morphology with the acceleration voltage of 100 kV, beam current of 60 mA and vacuum of 133.32 ~ 1 333.2 Pa was studied. A coaxial helium shielded welding process is proposed. During the welding of low carbon steel, the whole process is stable. The weld penetration is 30 ~ 40 mm, and the electron beam welding joint with large aspect ratio is obtained.