Abstract: Electron beam is a new surface modification technology of energy-carrying beam, which can effectively improve the surface structure and properties of materials. The surface modification of 40Cr steel was carried out by continuous scanning electron beam, and the effects of different electron beam currents on the surface microstructure and mechanical properties of 40Cr steel were studied. The results show that the cross-section morphology of the sample can be divided into three areas: the molten layer, the heat-affected zone and the matrix after the surface modification of the scanning electron beam. The microstructure of the melt layer and heat-affected zone is mainly composed of acicular martensite and lath martensite with fine and uniform grain size. When the beam is 4 mA, the surface roughness of the sample decreases from 2.306 μm to 1.469 μm, and the surface roughness decreases first and then increases with the increase of the beam. When the beam is 6 mA, the surface microhardness is up to 756.5 HV, which is 2.44 times of the matrix hardness. With the increase of the beam, the surface microhardness increases nonlinearly.