In order to solve the problem of acidification and corrosion of subsea oil production equipment, a green piperazine Mannich base chitosan derivative corrosion inhibitor CS-N-MB was synthesized in this paper, and its corrosion inhibition performance on N80 steel in 15wt.% hydrochloric acid solution was studied, and its mechanism of action on the metal surface was calculated. Using kojic acid and N-methylpiperazine as raw materials, Mannich base (MB) was synthesized through Mannich reaction, and then the Mannich base was grafted onto chitosan molecules. The synthesized products were characterized by infrared spectroscopy, and the corrosion inhibition ability of CS-N-MB on N80 steel in this strong acid environment was evaluated by electrochemical method and static weight loss method. The reactivity of chitosan (CS) and CS-N-MB was studied based on density functional theory, the active sites were clarified, and the adsorption energy of the corrosion inhibitor and the mean square displacement of water molecules in the system were calculated by molecular dynamics. The corrosion inhibition effect of N80 steel was good in the environment of 15 wt% hydrochloric acid, and when the corrosion inhibitor dosagewas less than 200 mg/L, the corrosion rate of N80 steel decreases gradually with the increase of concentration. When the addition of corrosion inhibitor was more than 200 mg/L, the corrosion rate of N80 steel increases slightly with the increase of concentration in a short time, but after 72 h, the corrosion rate of N80 steel decreases slightly and tends to be stable. Electrochemical studies showed that CS-N-MB can inhibit both cathodic and anodic reactions of corrosion simultaneously, and was a mixed inhibitor. Molecular simulation results show that the main active sites of CS-N-MB were concentrated in N, O and ring structures, and the movement of water molecules in the system was slowed down after adding CS-N-MB, which inhibits the occurrence of metal corrosion. CS-N-MB was a green corrosion inhibitor with good corrosion inhibition effect in strong acid environment. Multiple active centers can form a dense protective film on the metal surface, thereby effectively inhibiting the corrosion of metal.