Abstract: Objective The semi-coke powder was selected from a factory producing semi-coke with high volatile bituminous coal under medium-low temperature carbonization and pyrolysis.The semi-coke powder was used to conditioning the excess sludge from waste water treatment plant.Based on the physicochemical properties analysis of semi-coke powder,raw sludge and treated sludge by semi-coke powder,concentrating,filtering and dewatering property of sludge was researched through experiments.Meanwhile,the mechanism of conditioning sludge with semi-coke was analyzed by Zeta potential,microscope,infrared spectrum and scanning electron microscope.The experimental results showed: when semi-coke dosage was 250%,the specific resistance of filtration decreased significantly from 3.22×10¹³m/kg (raw sludge) to 4.33×10¹¹m/kg,the water content of sludge after concentration was reduced from 98.6% to 91.2%,the settling velocity of sludge obviously accelerated from 3.0mL/min to 34.3mL/min,the water content of filter cake was low down from 87.8% to 63.6%,and the low calorific value of sludge increased from 10.68MJ/kg to 21.77MJ/kg.The mechanism of semi-coke powder conditioning sewage sludge were adsorption and flocculation abilities to improve the settling performance,skeleton construction forming rigid frame structure with many channels and intervals which could prevent sludge cake compression and maintain high permeability during air-pump filtration,weakening the hydrophilicity and increasing the hydrophobicity of sludge.