The invention discloses a preparation method of a Schiff-base corrosion inhibitor by condensation of o-oxy-acetate-benzaldehyde and substituted aniline. The Schiff-base corrosion inhibitor is a solution formed by water and a product generated from condensation of o-oxy-acetate-benzaldehyde and substituted aniline. In terms of structure, the Schiff base contains an acid group, imino and two phenylrings. As the molecular system forms a large Pi-Pi conjugate, the Schiff base is stable and is not easy to decompose. As the structure is easy to accept exotic electrons, it has strong coordination ability, and compact and stable assembled monolayers can be formed on the surface of metal, thus effectively inhibiting corrosion to metal. Based on the characteristic, the Schiff-base corrosion inhibitor can be applied to prevent a steel material from being corroded. The corrosion inhibitor provided by the invention is simple to prepare, is convenient to use, contains low toxicity, is high efficient, generates no pollution to the environment, and has good corrosion inhibition of the No. 20 carbon steel.