Abstract: An analysis on the corrosion of bottom plate of floating roof tank (No.17 tank located at the tank farm in Changling Oil Refinery, Hunan province) has been made. The analytical results display that the physicochemical properties of oil, welding quality of the tank, long-term loading and unloading at low level, and material behavior and defects of steel plate result in the corrosion of the tank. Some countermeasures against the corrosion have been put forward in the paper.