<p>Polyimide (PI), a high-performance engineering polymer, finds common application across diverse fields such as the aerospace industry, medical devices, and electronic sensors. Beyond these uses, the presence of its characteristic heterocyclic imide functional group imbues PI with excellent corrosion inhibition effects. Here we reported the design, synthesis, and characterization of a novel, flexible, and superior corrosion-resistant polyimide coating specifically for low-alloyed mild steel. To ensure optimal formability and flexibility, a long-chain aliphatic unit was carefully integrated into the polymer matrix backbone. We comprehensively explored the applicability of this synthesized PI as an anti-corrosion coating on mild steel through both electrochemical investigations and advanced computational studies. The results were highly promising. Electrochemical impedance spectroscopy (EIS) evaluations unequivocally demonstrated significant corrosion resistance. The coating achieved a total resistance to corrosion (Rt) value exceeding 4 MΩ cm² even after 15&#xa0;days of immersion in a 3.5% NaCl solution. Furthermore, a neutral salt spray test revealed that after 500 hours of continuous exposure, the coated mild steel surface exhibited only 10% corrosion spots. This superior protective performance is primarily attributed to the exceptional barrier corrosion resistance property of the PI film, which effectively hinders the attack of corrosive ions. Complementing the experimental findings, density functional theory (DFT) calculations illustrated that PI strongly adsorbed onto the mild steel surface through both physical and chemical forces, concurrently facilitating the desorption of water molecules. This strong theoretical agreement further validates the experimentally observed notable corrosion resistance of the PI coating.</p>