The pressure of ultrafiltration membrane is usually 0 ? 0.02 ~ 0.3MPa, effectively remove suspended solids, colloidal particles, bacteria and most viruses in the water, and the removal rate of organic matter is 0 ? 20 ~ 60% and almost no rejection of small molecule organic matter and inorganic ions. At present, it has been widely used in drinking water, industrial water treatment, beverage, environmental protection, chemical industry, metallurgy, food and other industries, especially in seawater desalination, pure water, drinking water treatment and other industries ? As a pretreatment method of reverse osmosis membrane system, ultra pure water can ensure the stable operation of reverse osmosis membrane and subsequent equipment.