Abstract: It has taken place several times at a power plant that the condensate return water temperature and the vacuum temperature of the sixth, seventh and eighth streets of theair-cooling condenser are much lower than that of other streets, accompanying water lever waving in the exhaust steam device. The flow condition of the condensate in ACC is analyzed with the exclusive method, which concludes that there is air leakage on the B side of the main condensate return water pipe of the three streets. Therefore, some measures against the leakage are put forward to address these issues.