Microwave　and　ultrasonic　are　used　as　pretreatment　technologies　of　sludge,　because　of　the　excellent　performance　on　improving　sludge　dewaterability.　This　study　focuses　on　viscosity　and　particle　size　of　sludge　to　study　by　numerical　simulation.　The　results　show　that　the　Settle　Volume　(SV),　viscosity,　and　the　moisture　content　of　the　sludge　reduced.　The　increase　in　the　Chemical　Oxygen　Demand　(COD)　concentration　also　indicates　a　significant　disruption　of　complex　floc　structures.　The　particle　size　of　sludge　ranged　from　33.55μm　to　28.98μm,　9.44μm　of　microwave　and　ultrasonic　pretreatment.　Three-dimensional　flow　field　in　the　centrifuge　on　the　dewatering　efficiency　of　structural　parameters　and　sludge　pretreatment　are　investigated　numerically　by　using　Computation　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.