Abstract: To improve the electropolishing quality of 18CrNiMo7-6 carburized steel surface modification layer, the electropolishing process analysis and test of 18CrNiMo7-6 carburized steel surface modification layer under different carburized layer depths were carried out. The results indicate that the mixed solution of concentrated phosphoric acid and concentrated sulfuric acid are selected as the electrolyte, the temperature is 40-45 ℃. Firstly, the surface quality of 18CrNiMo7-6 carburized steel is studied under different polishing voltage, polishing current and polishing time. The optimal electropolishing parameters of 18CrNiMo7-6 carburized steel surface is obtained as 10 V, 1.8-1.9A and 70 s, and then the optimal parameters of the surface are finely tuned to obtain the optimal electropolishing parameters under different carburizing depths, the parameters of subsurface electropolishing is 10 V, 1.6-1.7 A and 65 s, and the parameters of core electropolishing is 10 V, 1.5-1.6 A and 60 s.