Th etryptophan and its compound were tested as corrosion inhibitors for carbon steel Q235 in an aqueous solution of 0.5 mol/L sulphuric acid by weight-loss and electrochemistry methods. The inhibitory mechanism was discussed by isothermal adsorption model and corrosion kinetics. The results show that single tryptophan has low corrosion inhibitor effect, while L-tryptophan and potassium iodide have certain synergistic effect, but synergistic effect with ascorbic acid is not significant. The three optimum amount of compound, the inhibition efficiency reaches 92.43%; The L-tryptophan and ascorbic acid are mixed type inhibitors, whereas the potassium iodide and complex inhibitors are the anodic type; Tryptophan is absvrbed on the surface of carbon steel by chemisorption adsorbed, in line with the Langmuir adsorption isotherm.