A　batch　of　tests　were　carried　out　to　investigate　the　effect　of　chironomid　larvae　on　sludge　reduction　and　activated　sludge　settling　performance.　The　results　indicated　that　chironomid　larvae　improved　the　activated　sludge　settlement　in　2　h.　The　Chironomid　larvae　reduced　the　settlement　of　activated　sludge　after　they　were　inoculated　in　15　min,　then　they　had　little　effect　on　activated　sludge　settling　performance　from　15　to　90　min.　Finally,　the　chironomid　larvae　improved　sludge　settlement　obviously　within　the　next　30　min.　The　chironomid　larvae　were　added　for　2　h　with　the　sludge　volume　of　36　%,　which　was　lower　than　the　sludge　volume　of　42　%　without　chironomid　larvae.　After　24　h　predation　of　chironomid　larvae,　the　sludge　concentration　had　a　reduction　of　12　%,　the　sludge　concentration　(MLSS)　reduced　from　1474　mg/L　to　1222　mg/L　with　the　MLVSS　reduced　from　1299　mg/L　to　1075　mg/L　correspondingly,　while　the　ratio　of　MLVSS　and　MLSS　maintained　at　87-88　%.　The　sludge　reduction　rates　with　the　predation　of　chironomid　larvae　were　2.31　g-MLSS/g-chironomid　larvae　(dry　weight)　s　d　and　1.75　g-MLVSS/g-chironomid　larvae　(dry　weight)　s　d　respectively.　©　2013　IEEE.