Reverse osmosis is the most sophisticated membrane liquid separation technology. The operating pressure is applied on the water inlet (concentrated solution) side to overcome the natural osmotic pressure. When the operating pressure higher than the natural osmotic pressure is applied to the concentrated solution side, the flow direction of the natural osmosis of water molecules will reverse, and the water molecules in the water inlet (concentrated solution) will become purified water on the dilute solution side through the reverse osmosis membrane; Reverse osmosis equipment can block all soluble salts and organic substances with molecular weight greater than 100, but water molecules are allowed to pass through. The desalination rate of reverse osmosis composite membrane is generally greater than 98%. They are widely used in the preparation of industrial pure water and electronic ultrapure water, the production of drinking pure water, boiler water supply and other processes. The use of reverse osmosis equipment before ion exchange can greatly reduce the discharge of operating water and wastewater.