Direct air-cooled power plant is popularized in north China because of the water conservation. Different from the water-cooled condenser, the ambient air absorbs the latent heat that turbine exhaust in the heat exchangers releases. In this paper, the numerical model of a 2×600MW power plant is prepared to simulate the performance of the air–cooled steam condenser under different wind speeds. Heat transferring with phase change is very complicated so that User Define Function(UDF) is applied to calculate the heat transfer rate in the air-cooled condenser. The fan flow rate will drop obviously during the increasing of the wind speed. As a result, the heat transfer rate between the steam and the ambient air also decreases and the pressure of the condenser rises. Finally, the stable condenser pressures under different wind speeds are predicted. The result shows that the air-cooled condenser is very sensitive to the wind speed.