Abstract: The corrosion of air-cooled condensers (ACC) commonly exists in the operating units in China. Though the ferric concentration of feedwater can be made to meet the standards by installing deferrization facilities, the ACC corrosion is not solved thoroughly. In this paper, the causes of such corrosion are analyzed. The conclusion of the analysis is that it is the extra low partition coefficient of ammonia and high acidic anion in the initial condensate that makes the corrosion happen at low pH values. The test results show that the ACC corrosion can be controlled using the methods of either adding a few organic base to the exhaust steam or raising the ammonia concentration of the feedwater; while considering the corrosion control and operation safety, the former one is a better option, in order to control the corrosion and ensure the ACC operation safely, it is better to add a few organic base to the exhaust steam than others.