The closed cooling water system at Zhongtian Co-founder of Energy Co., Ltd. is one of the few super large closed circulation cooling water systems in Chinese chemical industry. The materials of the system include carbon steel, stainless steel and aluminum. Desalted water is used as makeup water, and the cooling water is highly corrosive. At the initial stage of unit startup, no agent was used in the closed circulation cooling water system, resulting in the corrosion of system and the increased total iron and turbidity. After using the automatic dosing system and water treatment agent of a company, the total iron, turbidity, corrosion rate and other water quality parameters of the system were well controlled.