To explore the corrosion inhibition performance of bis-imidazoline (PMA) and 2-mercaptoethanol (MAT) in a CO2/O2 environment, infrared spectroscopy, weight loss method, electrochemical measurement technology (impedance spectroscopy and polarization curve) and scanning electron microscope were used to evaluate the inhibition behavior of PMA and MAT on the corrosion of carbon steel. Through quantum chemical calculations and molecular dynamics simulation, the active sites of PMA and MAT are analyzed. The results show that the maximum corrosion inhibition rate is 66.47% when PMA is 100 mg/L in a CO2/O2 environment. As the concentration of MAT increases, the corrosion rate decreases, and the corrosion inhibition efficiency increases. MAT with a concentration of 40 mg/L shows the best corrosion inhibition rate (70.38%), and the electrochemical results are consistent with the weight loss results. Electrochemical tests show that PMA is a mixed corrosion inhibitor, after the addition of MAT, the corrosion inhibition efficiency increases. In the presence of the combined PMA and MAT inhibitor, the corrosion of carbon steel is mainly controlled by the charge transfer process. From the SEM image, corrosion is obviously suppressed after adding PMA and MAT inhibitor. Combined with quantum chemical calculations and molecular dynamics simulation, the active sites of PMA are on the imidazoline rings, while the active sites of MAT are mainly on the sulfur atoms. The corrosion inhibition mechanism is due to that protective film first formed on the surface of the carbon steel, however, the protective film may have defects. After adding MAT, its smaller molecular size can fill the defects in the film, and the active site S atoms are adsorbed on the metal surface to make the film more compact and thus increasing the inhibition efficiency. Due to its strong adsorption capacity and hydrophobic properties, PMA has a good corrosion inhibition effect in CO2/O2 environment, and has a good synergistic effect with 2-mercaptoethanol, which can more effectively inhibit the corrosion process.