Triazine derivatives, 3-(4-thioxo-1,3,5-triazinan-1-yl) propanoic acid (TPA) and 1,5-diphenyl-1,3,5-triazinane-2-thione (DTT), were synthesized by a one-step synthetic process and utilized as high efficiency corrosion inhibitors for carbon steel (CS) in the oil production. Experimental tests demonstrate that both TPA and DTT show superior inhibition performance, with inhibition efficiencies (IEs) of 97.8% and 99.1%, respectively. GFN-xTB calculations reveal the adsorptions of TPA and DTT on CS surface through the S, N, O atoms of TPA, or the S, N atoms and phenyl ring of DTT. The most stable adsorption configurations of TPA and DTT are at an inclined angle of 15^o between the thiourea fragment and steel surface, which are determined with different initial adsorption configurations. The presence of phenyl ring in DTT not only endows it with stronger hydrophobicity, but also facilitates its strong absorption on CS surface by forming multiple Fe–C bonds through the π-electrons in the phenyl ring, which accounts for the better inhibitive effect of DTT. Additionally, the presence of H₂O solvent deteriorates the adsorptions of TPA and DTT due to the weak interactions between the TPA/DTT and H₂O molecules, which is demonstrated by the more positive adsorption energy and longer bonding distances of TPA and DTT on Fe surface.