Objective To find new inhibitors of carbon steel corrosion in gas-field wastewater. Methods The synergistic inhibition effect of mannich ( MABS) and thiourea ( TU) on N80 carbon steel in corrosion system of gas-field wastewater was investigated by using polarization curves and electrochemical impedance spectroscopy ( EIS) . Results The results showed that TU had strong inhibition effect on the anodic and cathodic processes of N80 steel corrosion, while MABS acted as mixed-type inhibitor preferentially restraining the cathodic process of metal. The combination of MABS and TU showed excellent synergistic inhibition effect in gasfield wastewater. When the Mannich and thiourea concentration was 0. 75% and 2. 5 mg / L, respectively, the inhibition effect was the best. Conclusion When using the combination of MABS and TU, a bi-layer inhibitor film with the inner layer of TU molecules and the outer layer of mannich molecules was formed on the N80 steel surface.