In recent years, many plant extracts have been used as green corrosion inhibitors to replace traditionalcorrosion inhibitors, but their inhibition performance still needs to be improved. The synergistic corrosioninhibition behavior and mechanism of maple leaves extract (MLE) and potassium iodide (KI) onQ235 steel in 0.5 M H2SO4 solution were firstly investigated in this work. The results demonstrate thatboth MLE and KI can prevent the corrosion of steel in corrosive media, and that their combined protectioneffect is superior. The corrosion inhibition efficiency (g) value reaches 93.4 % in corrosive solution withthe combination of 200 mg/L MLE and 200 mg/L KI, while the maximum of g is only 81.6 % using MLEalone. In addition, Fe-N bond and Fe-O bond were found on the steel surface through the X-ray photoelectronspectroscopy (XPS) analysis, which confirm the formation of a protective film. The adsorption behaviorof an inhibitory film composed of MLE and KI mixtures onto steel surface follows the Langmuiradsorption isotherm model, consisting of physisorption and chemisorption. Finally, molecular dynamics(MD) simulation indicates that inhibitor molecules can adsorb on the Fe substrate in a parallel way withhigh binding energy values, which supports the experiments well.