In order to deeply understand the corrosion inhibition mechanism of thiourea-based acidizing corrosion inhibitors and improve the application effect of corrosion inhibitors in acidizing development process，the corrosion inhibition performance and corrosion inhibition mechanism of two thiourea derivatives，such as phenyl thiourea（PHTU）and benzoyl thiourea（BOTU）on 20# steel in 15% HCl solution were studied by corrosion weight loss experiment，scanning electron microscope and quantum chemical calculation. The results showed that PHTU and BOTU had good corrosion inhibition effect on 20# steel in 15% HCl solution. When the concentration of corrosion inhibitor was 2 mmol/L，the dense and complete corrosion product formed on the surface of steel sheet could inhibit the contact between corrosive medium and steel substrate. The corrosion inhibition rate could reach more than 83%. Moreover，with the presence of C=O double bond in BOTU molecule，the corrosion inhibition performance of BOTU was better than that of PHTU. The adsorption of both PHTU and BOTU on steel surface was in accordance with the Langmuir adsorption model. The adsorption mode was a mixture of physical and chemical adsorption coexisting. Quantum chemical calculations showed that the reactive sites in corrosion inhibitor molecule mainly distributed on C=S double bond，C—N bond and C=O double bond of BOTU. Nitrogen atoms protonated by the acid could form physical adsorption with steel surface through electrostatic gravitational attraction. The C=S bond，C=O bond and phenyl group with high electron cloud density could provide electrons to form chemisorption with the empty d orbitals of Fe atoms through coordination and feedback bonding，which in turn stabilized the adsorption on metal surface to form a protective film and inhibit the corrosion process.