The "ion exchange method" for preparing pure water is widely used in China. The principle is that the cation (metal ions such as calcium, magnesium, copper and sodium) and anion (non-metallic ions such as carbonate, nitrate and sulfate) generated by the ionization of various inorganic salts in raw water pass through the cation and anion resin layers (ion exchange agent in the ion exchange column), and are adsorbed by the resin through displacement reaction with hydrogen ions and hydroxide ions on the resin. The hydrogen ions replaced from the resin and hydroxyl ions combine to form water molecules (H2O), so as to achieve the effect of removing inorganic salts in the water and achieve the purpose of preparing desalted pure water. With the operation of the ion exchange column, the replaceable hydrogen ions and hydroxyl ions on the resin in the column become less and less, and the displacement capacity becomes weaker and weaker. When the displacement capacity is weak to a certain extent, we call the resin "invalid", and then the resin needs to be regenerated. Regeneration is to let strong acid (commonly used HCL solution) and strong alkali (commonly used NaOH solution) ionize to generate hydrogen ions and hydroxide ions. When passing through the cation and anion resin layers, the inorganic salt ions adsorbed on the resin are replaced, and flow out of the ion exchange column with the acid or alkali solution, so that the resin in the ion exchange column recovers its original displacement capacity.