The adsorption behavior of different concentrations of sulfamethoxazole and tinidazole on 45 steel surface is analyzed by establishing a Temikin isotherm equation-based segmentation adsorption model, when they are used as corrosion inhibitors in 3% HCl solution. Adsorption parameters obtained by the model show their corrosion inhibiting performance increase first and then decrease as their concentrations increase. And the main reason is the intermolecular hydrophobic attractive force in high concentration range of inhibitor is stronger than the electrostatic repulsion, and then hydrophobic aggregation happens, resulting in the decrease of adsorption performance on the surface of 45 steel.