Sewage and water-soluble polymer are fully mixed, so that fine matter, chroma, organic matter and so on in sewage are gathered together; By using micro-nano bubble targeted capture technology, the flocculated substances in sewage can float on the surface of water and be collected uniformly. The fine substances that did not float in the water were intercepted and removed by deep filtration of the plant fiber cake membrane. A large number of functional groups rich in the surface of plant fiber were used to adsorb and remove residual chromaticity, biological and chemical pollutants in sewage.