Hydrocyclone is a liquid-liquid separation equipment commonly used for produced water treatment in oil fields. It is mainly used to separate those free oil droplets suspended in liquid to meet the standards required for disposal by regulations. The strong centrifugal forces generated by the pressure drop is to achieve high-speed swirling effect on the liquid in the cyclone tube, thereby centrifugally pushing the heavy liquid (water) to the inner surface, while the light liquid (oil) is squeezed to the center of cyclone tube. With internal pressure gradient which then push the heavy liquid (water) moving downwards while the light liquid (oil) to the upwards. As such, the oil particles with lighter specific gravity is separated from feed water and achieving the purpose of oil-water separation. Hydrocyclones are widely used in petroleum, chemical industry, environmental protection and other fields or industries. They can efficiently handle various liquids with different specific gravity, improve production efficiency and reduce pollutant emissions.