High toxicity is the main reason to limit the application of traditional corrosion inhibitors. Herein, the development of a green and high-efficiency alternative to displace traditional and hazardous corrosion inhibitor is an urgent task. Cauliflower extract (CFE) has the potential ability to solve this problem because it comes from nature and also contains plenty of heterocyclic organics. Therefore, CFE, as an eco-friendly corrosion inhibitor, was prepared for the first time via a simple and green extraction method. The typical electrochemistry and scanning vibrating electrode technology (SVET) tests prove that CFE can effectively inhibit the copper corrosion in 0.5 M H2SO4. What's more, this inhibition effect is still strong when prolonging the immersion time, and the highest inhibition efficiency reaches up to 99% at 48 h. Based on the surface composition analysis result, it can be obtained that CFE protective film is formed on the copper substrate, and thereby significantly block the active corrosion sites of copper. Furthermore, the parallel adsorption state and high Ebinding value from MD simulation imply the powerful interaction between CFE molecules and Cu, which is crucial evidence to explain the inhibition effect of CFE for copper at the molecular level. Display omitted •A green cauliflower extract (CFE) as corrosion inhibitor was prepared via a green and simple extraction method.•The high and sustainable anti-corrosion ability of CFE for copper was achieved.•Strong adsorption happened between CFE molecules and copper surface.•The anti-corrosion mechanism of copper with CFE was explained in detail.