Abstract: 304 stainless steel plates with thickness of 3 mm were welded by vacuum electron beam welding under accelerating voltage of 120 kV, focus current of 2 460 mA, and welding current of 12 mA.The effects of welding speed (10-40 mm·s^-1)on microstructure and mechanical properties of the joints were studied.The results show that microstructures of the weld mainly consisted of columnar grains at both sides and equiaxed grains in center.With increasing welding speed, the grains size of the weld decreased, the volume fraction of ferrite increased, the hardness of all areas in joints increased, the tensile strength increased first and then decreased, and the fracture of joints all occurred at base metal after tension.Under the experimental conditions, the optimal welding speed for 304 stainless steel by the vacuum electron beam welding was 30 mm·s^-1; at this time the welded joint had good forming quality with ferrite volume fraction of 7.4%, relatively high hardness, and the largest tensile strength of 640 MPa; the tensile fracture showed the characteristics of ductile fracture.