The work aims to provide the theoretical basis for the service of Al coating by studying the corrosion behavior of thermal-sprayed Al coating in different positions of the sewage storage tank. Al coating was deposited on the surface of Q235B steel via supersonic arc spraying. Scanning electron microscopy (SEM) was employed to analyze the microstructure and morphology of the Al coating before and after corrosion and the energy dispersive spectrometer (EDS) was used to characterize the elemental compositions in the coating. The corrosion behavior of coating at different positions of the tank (water/air interface, water phase, water/mud interface and mud phase) was characterized via the thickness reduction rate and corrosion microstructure. The Al coating presented a typical lamellar structure with the porosity of 5.4% and the thickness of 60 μm. Additionally, the coating had no evidently oxidation. After immersion for 60 days, the surface of the coating in the water/air interface and the water phase environment still maintained typical characteristics of the as-sprayed coating, i.e. the smooth area formed by droplet spreading and the rough area formed by droplet splashing. The corrosion form of the coating was uniform corrosion because the clogging isolation of the initial products formed oxide film on the coating surface. Due to the factors, such as oxygen concentration corrosion, the corrosion rate of coating oxide film in the water/mud interface and the mud phase environment was higher than passivation rate. The coating had serious localized corrosion, and showed some cracks and spallation during immersion in the water/mud interface and the mud phase. The local corrosion caused by integral peeling of one or several layers of flat particles mainly occurred. In addition, the splat particle interfaces inside the entire coating in the mud phase corrosion environment were all completely corroded, which induced the generation of loose coating. The corrosion mechanism of Al coating in the sewage storage tank is different from that in the ocean. The corrosion mode of anodized Al coating protecting the storage tank is different from that of ordinary tanks. However, the failure positions of supersonic arc spraying coating in sewage storage tanks of the experimental environment are all the mud phase.