Abstract: The electron beam welding of 15Mn alloy steel plate was carried out after the applied magnetic field was set in weld depth direction, perpendicular to welding direction and along welding direction, respectively. The effect of the applied magnetic field on the electron beam weld formation, microstructure and properties was studied. The results show that the electron beam weld quality was good under different applied magnetic field condition, and no crack, porosity and slag welding defects existed. When the magnetic field direction was perpendicular to welding direction or along welding direction, the weld was deflected in both surface and depth direction. Under the condition of magnetic field direction along the weld depth direction, the depth and width of the weld increased, compared with those without applied magnetic field. Under the condition of magnetic field direction along the welding direction, the depth of the weld unchanged, the width increased, and the deflection angle in depth direction was relatively small. Under the condition of magnetic field direction perpendicular to the welding direction, the depth of the weld decreased, the width increased, and the deflection angle in depth direction was relatively large. The weld microstructure and distribution of section microhardness was not affected by the direction of the applied magnetic field.