To improve the corrosion-protection performance of polyaniline (PANI) coating and clarify its anti-corrosion mechanism, modified graphene oxide (GO) was used as reinforcement to improve the performance of PANI coatings. GO was functionally modify by in-situ polymerization of PANI, whose growth state on the GO surface was regulated. The structure and morphology of functionalized GO were characterized and analyzed by Fourier infrared transform spectrometer (FTIR), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS), Raman spectrometer (Raman) and field emission high-resolution scanning electron microscope (FESEM); Then functionalized GO was introduced into the PANI coating and prepared PANI/GO composite coatings. Electrochemical impedance spectroscopy (EIS) was used to study the corrosion protective effects of PANI coatings and different PANI/GO composite coatings on stainless steel substrates and discuss their corrosion resistance mechanisms. The results show that PANI grows uniformly on the GO sheets, and its structure and morphology can be effectively regulated by controlling the amount of aniline. Moreover, the in-situ polymerization of PANI promotes the peeling and stretching of the GO sheets and improves its dispersion and compatibility in the coating. Compared with the pure PANI coating, the PANI/GO composite coating has a larger stable open-circuit voltage value, and when the mass ratio of aniline to GO is 5∶1, the dispersion effect of functionalized GO is optimal and the enhancement effect for the anti-corrosion protection performance is also the most. At this time, the composite coating exhibits the largest capacitive reactance arc diameter, highest charge transfer resistance and smallest electric double layer capacitance. In conclusion, PANI coating can form a protective layer with a shielding effect on the metal surface, but its non-compact morphological structure and molecular configuration changes under corrosive environment limit the corrosion protection performance of the coating. The introduction of functional structured GO, especially under the condition of the best GO dispersion, can effectively improve the compactness and anti-permeability of the coating, and further inhibit the damage of the coating structure due to the molecular configuration changes caused by the proton reaction, thereby enhancing the corrosive protection performance of the coating.