In　order　to　imporve　the　activated　sludge　settling　performance　by　using　chironomid　larvae　(CL),　the　effect　and　mechanism　of　CL　on　activated　sludge　settling　performance　were　investigated　in　this　study.　The　results　show　that　the　adding　of　CL　enhances　the　sludge　settling　performance　in　a　short　time.　The　improvement　performance　becomes　significant　as　the　CL　density　increased　from　0.2　to　1.2　g　wet　mass　of　CL　per　g　dry　mass　of　activated　sludge.　There　is　a　suitable　sludge　concentration　(5　g/L)　in　achieving　settleability　improvement　at　the　same　CL　density　(1.0　g　wet　mass　of　CL　per　g　dry　mass　of　activated　sludge).　The　introduction　of　CL　reduces　the　contents　of　protein　and　polysaccharide　and　the　ratio　of　protein　to　polysaccharide　in　extracellular　polymeric　substance　(EPS),　which　is　probably　the　main　reason　for　CL　improving　the　sludge　settling　performance.　Furthermore,　the　long-term　experiment　confirms　that　adding　the　supernatant　from　the　CL　reactor　to　the　sequencing　batch　reactor　(SBR)　for　treating　domestic　wastewater　reduces　the　sludge　volume　index　(SVI)　from　120　mL/g　to　60　mL/g.　©,　2015,　Beijing　University　of　Technology.　All　right　reserved.