To interpret the role of hydrophobic chain of imidazoline in the corrosion protection of steel, two kinds of imidazoline corrosion inhibitors with highly different hydrophobic chain length were selected as the research objects. The influence of hydrophobic chain length on the corrosion inhibition performance of imidazoline corrosion inhibitors was investigated using computer molecular dynamics simulation and quantum chemical calculation methods. Molecular dynamics simulation results show that the carbon chain prevents water molecules from approaching the iron surface during the adsorption process. The quantum chemical calculation results show that the rise of the hydrophobic chain length increases the mass and electron supplying capacity of the molecule, and boosts the interaction between the molecule and iron, which effectively inhibits the tendency of iron to lose electrons due to corrosion. The research results indicates that imidazoline corrosion inhibitor hydrophobic chain plays an important role in the corrosion protection of iron.