Chemical mechanical planarization (CMP) can enable the overall subnanometer flatness of copper to meet the needs of integrated circuits, but the slurries used in CMP still face challenges in terms of being "green" due to the use of highly toxic corrosion inhibitors. Although some eco-friendly corrosion inhibitors have been reported, most of them are expensive for industrial applications. Herein, fulvic acid, a cost-effective and eco-friendly biomass, is employed as an alternative corrosion inhibitor to achieve green CMP of copper. The underlying corrosion inhibition mechanism is systematically investigated by combining electrochemical analysis, DFT calculations, and XPS. The results show that fulvic acid can inhibit corrosion by adsorbing on the reduced and oxidized copper surfaces through a coordination bond, back-donation, and electrostatic interaction. Meanwhile, the copper ion-fulvic acid complexes formed during the CMP process can also cover the copper surface, thus limiting excessive corrosion reactions. Consequently, Cu2O dominates the oxides on the final copper surface after CMP. By using fulvic acid-based slurry, a surface roughness of 0.232 nm can be achieved in an acidic environment, which is almost atomic-level copper surface and better than the vast majority of reported studies. Thus, fulvic acid should be one promising corrosion inhibitor for green CMP of copper and is most likely applicable to other metals and alloys.