Abstract: In this paper, 30CrMnSiA steel plate with 1.8mm in thickness was welded by vacuum electron beam welding, which are applied extensively in aerospace industry. The effect of welding parameters on the shape microstructurs and mechanical properties of joint were investigated. The results show that the fine weld shape can be obtained within a wide range of process parameters. The microstructure of weld metal is a typical lath martensite and the 600HV microhardness can be achieved, which is far higher than that of the base metal (300HV). Meanwhile, the tensile strength of the vacuum electron beam welded joint can arrive a value of 1400MPa, and the fracture of all tensile sample were occurred in the heat affected zones.