Mixing is an effective strategy to improve the inhibition performance of corrosion inhibitors based on their synergistic effect. In this work, the synergistic inhibition effect of S-benzyl-L-cysteine (SBLC) and thiourea (TU) on the corrosion of carbon steel in the CO2-saturated oilfield produced water is studied by electrochemical tests and surface analysis. It is found that SBLC and TU exhibit a significant synergistic corrosion inhibition effect. Meanwhile, the synergistic mechanism is in-depth elucidated by theoretical calculations. The intermolecular interaction between SBLC and TU molecules leads to the formation of a more compact and stronger adsorbed film on carbon steel surface. Display omitted •Amino acid (SBLC) and thiourea (TU) were tested as compounded corrosion inhibitors for carbon steel in CO2 environment.•Electrochemical tests indicate that SBLC and TU exhibit significantly synergetic inhibition effect.•The adsorption of SBLC and TU on carbon steel surface is significantly strengthened after mixing.•The co-adsorbed SBLC+TU mixture film can effectively prevent the diffusion of corrosive particles to carbon steel surface.•Theoretical calculations were performed to in-depth explore the synergetic mechanism of SBLC and TU.