The work aims to study corrosion inhibition effect and mechanism of osmanthus fragrans fruit extract on Q235 steel in 0.5 mol/L sulphuric acid solution medium. The inhibition performance of osmanthus fragrans fruit extract to Q235 steel in 0.5 mol/L sulphuric acid solution medium was studied in electrochemical methods including weight loss method, polarization curves and electrochemical impedance spectroscopy (EIS). Effects of osmanthus fragrans fruit extract concentration on inhibition efficiency at 25 ℃ were investigated extract. The inhibition mechanism extract was discussed as well. The osmanthus fragrans fruit extract prepared with 95% alcohol as extractive solvent exhibited excellent corrosion inhibition effect on Q235 steel in 0.5 mol/L sulphuric acid solution medium. The inhibition efficiency increased as the concentration of osmanthus fragrans fruits extract increased, and the inhibition efficiency was up to 92.90% when the concentration of osmanthus fragrans fruit extract was 10 g/L. Electrochemical test results showed that the osmanthus fragrans fruits extract was a mixed-type inhibitor which inhibited corrosion of Q235 steel mainly by inhibiting hydrogen evolution process on the cathode, and the inhibition mechanism belonged to geometric blocking effect. The adsorption of effective inhibition part on the Q235 steel surface accorded with the Langmuir isothermal equation, and the adsorption equilibrium constant was 1.09 L/g. The osmanthus fragrans fruits extract is a natural and green corrosion inhibitor having wide application prospect, which has significant corrosion inhibition effect on Q235 steel in 0.5 mol/L sulphuric acid solution medium.