Ultrafiltration is a membrane separation process based on the principle of sieving separation and pressure as the driving force, and the filtration accuracy is in the range of 0.005-0.01μm, which can effectively remove particles, colloids, bacteria, heat sources and polymer organic substances in water. It can be widely used in the separation, concentration and purification of substances. The ultrafiltration process has no phase conversion, operates at room temperature, is particularly suitable for the separation of heat-sensitive substances, and has good temperature resistance, acid and alkali resistance and oxidation resistance, and can be used continuously for a long time under the conditions of 60 °C and pH of 2-11. The ultrafiltration process can be divided into three types: batch operation, continuous ultrafiltration (CUF) and refiltration. Intermittent operation has maximum transmittance and high efficiency, but low throughput. The continuous ultrafiltration process is often carried out under partial circulation, and the circulating volume in the circuit is often much larger than the amount of feed liquid, and is mainly used in large-scale treatment plants. Heavy filtration is often used for the separation of small and large molecules。