Abstract:The 10 um plankton sampling network was used to survey the microfauna in the outflow of granular active carbon (GAC) filter in A plant, which showed that the dominant species were Rotifera, Nematode, Oligochaeta and Crustacea. When the thickness of quartz sand filter layer was 40 or 50 cm, the grain size was 0.3-0.5mm and the flow rate was 10-12 m•h-1, more than 50% of the large metazoan, such as rotifera, crustacean, and oligochaeta, could be intercepted, but few nematode could be intercepted. It was suggested that the 10 um microstrainer should be added after the chlorine chamber, and this enhanced filtration could reduce the risk of microfauna leakage by one grade and the work cycle could reach 96 h.