Abstract: A new Mannich base corrosion inhibitor (MHX) was prepared by Mannich reaction with formaldehyde, benzylideneacetone and p-methylaniline as raw materials. The preparation conditions were optimized by orthogonal test.The effects of MHX addition on the corrosion inhibition of N80 steel in HCl solution were studied by static weight loss method, electrochemical test and molecular dynamics simulation. The results showed that the corrosion rate of N80 steel sheet was 2.6 g ·m^-2 ·h^-1 and the corrosion inhibition rate was 99.63 % in 20 % HCl solution with 1% MHX at 90 ℃. The corrosion inhibitor was a mixed type corrosion inhibitor which mainly inhibited the anode, it could greatly reduce the corrosion current density and improve the electrode impedance. MHX could adsorb and form film on the surface of N80 steel, reduce the loss of Fe on the surface of steel, and reduce the surface roughness to 93.81 nm. The adsorption energy of MHX molecule on N80 steel surface was -7.59 eV, which could effectively replace H₂O molecule and adsorb on the metal surface, thus playing a role in corrosion inhibition.