In the process of wastewater in contact with the filtering media, among the organics is assimilated by microorganism, it become the biological-membrane in the surface of filtering media, the biological-membrane is highly dense material, it is Ecosystems that is composed of Aerobic bacteria, Anaerobes,Facultative bacteria,Fungus,Protozoan and Higher animals. The biological-membrane adsorb the organics in water, then, the Aerobic bacteria decompose it.The inner and outer of biological-membrane deliver the many variety of substances, the process as following: the oxygen in the air dissolve in the flowing water layer, through the water layer to transmit oxygen for the biological-membrane in order to supply the breathing of microorganism, the flowing water layer deliver the organics in wastewater to the adhesion water layer, and the organics enter into biological-membrane, to be decomposed; the Metabolites of microorganism is discharged in the opposite direction. The dissolved in water organics is metabolized by microorganism, adsorbed, Oxidative decomposition, in order to get the purification.