The　horizontal　decanter　centrifuge　is　widely　used　in　the　process　of　sludge　dewatering,　the　dewatering　efficiency　of　which　is　significantly　influenced　by　structural　and　operating　parameters,　as　well　as　material　properties.　Sludge　modification　is　very　important　for　sludge　dewatering,　and　it　has　a　greatly　influence　on　sludge　dewatering　characteristics.　The　basic　theory　and　the　structural　features　of　centrifuge　and　sludge　modification　technology　are　studied　for　the　separating　efficiency.　The　three-dimensional　flow　field　in　the　centrifuge　of　structural　parameters　and　spiral,　and　sludge　modification　on　the　dewatering　efficiency　are　investigated　numerically　by　using　computational　fluid　dynamics　(CFD)　software　FLUENT.　The　results　show　that　improvement　of　separation　efficiency　can　be　achieved　by　not　only　increasing　the　length-diameter　ratio,　but　also　decreasing　the　sludge　viscosity.　In　addition,　the　centrifuge　with　spiral　or　not　with　spiral　has　large　impact　on　the　simulation　result,　which　should　be　noticed　in　the　investigation.　©2014　Journal　of　Mechanical　Engineering