Abstract: Nowadays SCAL indirect air cooler system is a tendency during the development of thermal power generation in the North area. However, the control of the water quality of its circulating water and corrosion protection has not been solved. In this work, the change of dissolved oxygen in circulating water and its effect on the corrosion of materials in this system was investigated by field survey, field simulated experiment. The results indicate that this system was confined during operation and oxygen in atmosphere could hardly diffuse into circulating water. Almost all the dissolved oxygen enter into the system with circulating water before operation. The corrosion of steel was the main reaction consuming oxygen in circulating water. The change of dissolved oxygen content in circulating water will lead to the mutual conversion of various crystalline carbon steel corrosion products and the absorption or release of impurity ions. Under the condition of low dissolved oxygen, the corrosion behavior of carbon steel will cause the pH value of intercooled circulating water to increase.