This series with secondary filtration can work under the high flowrate and high filtering precision conditions in the areas of field water flooding, electric power, pharmaceuticals, high-standard edible water supply, and chemical solution filtration. First class is rough filtration that employs high power permanent magnetic core so as to effectively remove the ferromagnetic matter in the media. Fine filtration is secondary, which adopts folding glass fiber filtering element, the solid content after filtration≤1mg/1, the particle diameter≤2um, total iron content≤0.5mg/1. For thc filtering medium Call conduct backwash. the product is especially suitable for the injection engineering in fields with low permeability and able to effectively filter out mechanical impurity to lower furthest its harm to the formation.