The work aims to synthesize starch-phenylethylene-methyl methacrylate graft copolymer (CS-PE-MMA) and prepare CS-PE-MMA molecular monolayer of good corrosion resistance to steel in citric acid by applying self-assemble technique. The morphology and composition of the self assembled molecular monolayer were characterized by scanning electronic microscope (SEM) and infrared spectroscopy (IR). The corrosion inhibition was studied by virtue of potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). A stable, orderly and dense molecular monolayer was generated on the cold rolled steel surface by CS-PE-MMA. Polarization curves show that reactions of anode and cathode of the working electrode were inhibited, EIS spectrum mainly showed the semicircular capacitive arc, the charge transfer resistance increased with the increase of CS-PE-MMA self-assembly temperature and time, highest inhibition rate was up to 73.04%. The CS-PE-MMA is a mixed type inhibitor and self-assembled molecular monolayer has a good corrosion inhibition to cold rolled steel in H3C6H5O7 solution.