It is a traditional water treatment process in which various anions and cations in water are replaced by anion and cation exchange resins. Anion and cation exchange resins can be used alone or in different proportions to form an ion exchange cation bed system, an ion exchange anion bed system, and an ion exchange mixed bed system. The mixed bed system is usually used as the terminal process for preparing ultrapure water and high-purity water after water treatment processes such as reverse osmosis. It is one of the irreplaceable means for preparing ultrapure water and high-purity water. Its effluent conductivity can be lower than 0.2μS/cm, and the effluent resistivity reaches more than 5MΩ·cm. According to different water qualities and use requirements, the effluent resistivity can be controlled between 5-18MΩ·cm. It is widely used in the preparation of ultrapure water and high-purity water in industries such as electronics, ion exchange resin systems, and boiler make-up water.