Abstract: Process the surface of 45 steel was carried out in order to significantly improve the surface roughness and comprehensive mechanical properties of 45 steel using electron beam micro melting polishing technology. The influences of electron beam polishing on surface roughness, microstructure and hardness of the modified layer were studied. The influences of electron beam scanning current and scanning speed on surface roughness and microstructure of modified layer was also discussed. The results show that the surface roughness of 45 steel reduced from 2.091 μm to 0.738 μm. The decrease rate is 64.7%. The surface modification layer can be divided into the polishing zone, the heat affected zone and the matrix zone. The microstructure of the polishing layer is acicular martensite with 950 ~ 913 HV hardness. The microstructure of the heat affected zone are acicular martensite and ferrite with 855 ~ 280 HV hardness. The microstructure of the matrix zone are pearlite and ferrite with a hardness of 244 ~ 204 HV. The influence of electron beam processing parameters on the surface roughness after polishing is significant. Under the corresponding polish effect condition, thickness of the modified layer increases with the increasing of the scanning current of electron beam, and decreases with the increasing of scanning speed.