This filter is suitable for hydraulic system oil return fine filtration, filter system due to wear, metal particles and seals produced by the rubber impurities and other pollutants, so that the oil return to the tank to keep clean. The filter is directly connected with the return oil pipeline by screw thread, and extends into the oil of the oil tank. The filter element adopts a new type of chemical fiber filter material, which has the advantages of high oil permeability, high filtering precision, small pressure loss and large pollution capacity.