In this paper, surface morphology characteristics of mechanical finishing (MF) and electrochemical mechanical finishing (ECMF) for 45# steel was investigated. The microcosmic geometry parameters were measured by Surfcorder SE-3H. Compared with original surface, the surface morphology characteristics of the workpiece machined by MF and ECMF have been analyzed with auto correlation function (ACF). The results show that there exist periodicity component in surface profile before and after finishing. The auto correlation curves of ECMF surface have a smaller average period compared with MF surface. The low-frequency component and the mean ripple peak distance of original surface profile are obviously decreased. Furthermore, the ripples and peak density are increased, ECFM have a higher efficiency compared with MF, and the surface roughness Ra is decreased from 0.231μm to 0.032μm in 1 minute. The results indicate that surface quality, material ratio of the profile and wear resistance machined by ECMF are improved obviously.