Pure Zn coatings easily lose their protective performance after biofouling because they have no antibacterial effect under visible light. In this study, we fabricate a new antibacterial Zn composite coating using electrodeposition to couple Fe3+-doped alkalized g-C3N4 (AKCN-Fe) into an existing Zn coating and show that the AKCN-Fe enhances antibacterial property of the Zn coating under visible light. We attribute this enhancement to the high photocatalytic performance, high loading content, and good dispersion of AKCN-Fe. In addition, the photocatalytic antibacterial mechanism of the composite coating is supported by scavenger experiments and electron paramagnetic resonance (EPR) measurements, suggesting that superoxide (·O2−) and hydroxyl radical (·OH) play main and secondary roles, respectively.