Colloidal　particle　and　microorganism　fragment　in　secondary　effluent　are　removed　well　by　dissolved　air　flotation.　The　first,　the　flotation　pretreatment　conditions　were　tested　and　the　results　indicate　that　the　flocculation　conditions　are　three　stirring　levels,　stirring　strengths　are　50/30/20　s-1　and　reaction　time　is　20　minutes.　The　second,　the　removal　efficiency　of　COD　and　turbidity　were　improved　as　the　dosages　of　polyaluminium　chloride　(PAC)　were　increased,　and　the　flotation　tank　has　better　ability　of　resistance　to　different　influent　load.　The　effluents　reach　Water　Quality　Standard　for　Urban　miscellaneous　Water　Consumption　(GB-T18920-2002)　and　Urban　Wastewater　discharge　standards　(GB-T18918-2002).　In　the　end,　the　test　shows　that　the　removal　efficiency　of　turbidity,　COD　and　TP　were　improved　to　43%,　42%　and　27%　respectively　when　the　surface　load　of　flotation　tank　reached　12.7　m3/(m2·h),　and　the　increasing　height　of　separation　zone　is　of　advantage　to　effluent　quality,　but　the　invest　of　tank　may　be　high.