The　high　moisture　content　of　sludge　is　harmful　to　the　environment　during　the　process　of　disposal　such　as　water　pollution　or　the　large　area.　Therefore,　sludge　pretreatment　is　very　important　before　the　mechanical　dewatering.　In　this　paper,　sludge　specific　resistance　(SRF)　and　moisture　content　of　the　cake　were　regarded　as　the　evaluation　parameters　of　sludge　de　watering.　Optimum　range　of　the　effect　factors　was　obtained　through　single　factor　experiment.　The　effect　of　ultrasonic　and　Calcium　oxide　on　sludge　de　watering　performance　was　investigated.　Multiple　quadratic　regression　equation　models　of　SRF　and　moisture　content　of　sludge　cake　were　established　by　Box-Behnken　experimental　design.　The　optimum　parameters　of　co-conditioning　demonstrated　that　ultrasonic　combined　with　Calcium　oxide　could　significantly　improve　sludge　dewatering　performance.　The　optimum　conditions　for　ultrasonic　time,　ultrasonic　density　and　Calcium　oxide　dosage　were　2.53　min,　0.33　W/mL　and　0.97　g/100mL,　respectively.　Calibration　experiment　was　conducted　under　the　optimal　conditions,　SRF　being　of　(2.33　+/-　0.37)x　10(12)　mg/K　and　moisture　content　of　the　cake　being　of　(65.07　+/-　0.57)%　could　be　achieved,　which　coincided　with　model　predictions.