Abstract: The CoO/polyaniline (PANI) composite coatings were synthesized in the electrolyte of CoSO₄-C₆H₇N-H₂SO₄ mixture by means of constant potential method. The effect of (H₄N)₂S on the CoO/PANI composite coating was studied, and corrosion resistance and microstructure of the CoO/PANI composite coatings were analyzed by combining electrochemical testing technology, SEM, XRD and accelerated corrosion tests. The results show that the CoO exists in the form of crystal in the CoO/PANI composite coatings. With the loading of (H₄N)₂S, the microstructure of the CoO/PANI coatings changes from irregular thin lamellar morphology into uniform dense contiguous lamellar morphology, when more (H₄N)₂S was added, a small amount of holes appear on the surface of the (H₄N)₂S-CoO/PANI composite coating. Self-corrosion current density of CoO/PANI composite film without (H₄N)₂S is 7.079×10^-6 A/cm², and self-corrosion potential is -0.545 V. After 0.3 g/L (H₄N)₂S is added, self-corrosion current density of the (H₄N)₂S-CoO/PANI composite coating is 7.943×10^-7 A/cm², corrosion potential is -0.314 V, polarization resistance is 6 426.8 Ωcm², corrosion time of 10% HCl drip reaches 478 s, and no rust is observed after 56 h of neutral salt spray test. Addition of (H₄N)₂S has obvious effects on corrosion resistance of the (H₄N)₂S-CoO/PANI composite coatings.