A novel method integrating electrochemical machining with mechanical action was proposed to polish the flexible metal foil to satisfy the requirements of thin-film solar cell flexible stainless steel substrate for lower surface roughness,higher light reflection rate and lower harmful impurity. Firstly, a compound cathode was designed and manufactured for machining flat surfaces, meanwhile its mechanism on the material removal was analyzed. Then, the electrochemical corrosion behaviors and friction effects were analyzed based on the Faraday law and adhesion friction theory, by which the match action between electrochemical corrosion and mechanical action was resolved. Finally, taking the 304 stainless steel sized 50 mm×50 mm×0.3 mm as the workpiece, an experiment was conducted to demonstrate above analysis. The results show that the surface roughness has changed from Ra124 nm to Ra10 nm and the reflection rate changed from 56.8% to 62.4% after polishing time of 20 min. Moreover, a metal oxide layer(Fe2O3,Cr2O3) is formed , which blocks the diffusion of Fe and Cr. These results indicate that the method proposed has higher efficient and economical to process thin film solar cells with flexible stainless steel foils.