Abstract: To broaden the application of polybenzoxazine resin in the field of metal anti-corrosion, main-chain benzoxazine (BA-ddm) and diamine-type benzoxazine (Ph-hda) were copolymerized to prepare novel polybenzoxazine copolymers, and the anti-corrosion properties of the copolymer coatings were mainly studied. BA-ddm and Ph-hda were prepared by the solution method, and a series of benzoxazine copolymers were prepared by mixing them at different mass ratios. Copolymer coatings (P(PB)) were prepared on the surface of tinplates by dip coating and heat curing methods. The structure and morphology of the copolymers were characterized by FTIR, ¹HNMR, DSC, optical microscopy, and SEM. The hydrophilicity and hydrophobicity of the copolymer coatings were analyzed by contact angle tests, and the anti-corrosion properties of the coatings were mainly studied by electrochemical tests. The test results of FTIR and ¹HNMR indicate that the benzoxazine copolymer coatings are successfully prepared. The DSC test results show that the introduction of BA-ddm containing phenolic hydroxyl groups promotes the copolymerization reaction of the two benzoxazine oligomers. The characterization results of optical micrographs and SEM show that all coatings are uniform and dense, indicating that dense protective coatings are successfully constructed. The hydrophilicity and hydrophobicity tests of the coatings demonstrate that the introduction of Ph-hda containing long aliphatic chains can endow the copolymer coatings with good hydrophobicity. When the mass ratio of BA-ddm to Ph-hda is 1:19, the water contact angle and water absorption of P(PB5) are 100.1° and 0.56%, respectively. The test results of dynamic polarization curves and electrochemical impedance spectroscopy (EIS) indicate that copolymer coatings with different ratios all have good anti-corrosion effects. Among them, the P(PB5) coating exhibits the best anti-corrosion property, its corrosion current density is 5.15 × 10⁻⁸ A·cm⁻², and the anti-corrosion protection efficiency reaches 99.23%; the impedance value of the coating at 0.01 Hz is 1.78 × 10⁷ Ω·cm², which is nearly five orders of magnitude higher than that of the blank tinplate.