Circulating water treatment agent is divided into chemical method and physical method. The cooling circulating water system mainly adopts chemical methods, including water treatment system, dosing system, cleaning system and backwashing system. The hardness and salinity of system make-up water are removed by ion exchange. Add scale inhibitor, corrosion inhibitor and bactericide to the combined circulating water, and regularly clean and backwash the system to form a complete set of water treatment technology. The method has good effect, can prolong the service life of the equipment, has high operation efficiency and saves energy. It has been applied by major companies at home and abroad, and has gradually adopted large-scale air-conditioning cooling water treatment system, which has broad prospects.