An air jet drying system composed of a turbo blower, an air ejector and three stage cyclones is constructed to produce a dried powder through water content reduction of dewatered cake obtained from sludge treatment process. The air flow to be ventilated by the turbo blower forms a high speed flow field by passing through the air ejector and a circulative flow field by passing through the cyclones. Dewatered cake, 100 mm in size, is disintegrated by jet and collision through passing the air ejector and becomes fragmented with size no more than 2mm. These fragmented particles follow air flow and are dried as moisture is evaporated from particle surface. A powder composed of 1.6 mm spherical particles is produced from pilot scale equipment of 1 ton/hr under the conditions of air velocity, maximum flow rate and air temperature profile of 84 m/sec, 180 m3/min and 73-28 ℃, respectively. The air dried powder with average water content of 49.8 wt% is recovered after drying the dewatered cake with water content of 83.3 wt% in a real operation, indicating 33.5 wt% decrease in water content. It is estimated that the power consumption of the air jet drying system requires 92 kWh/Ton to reduce the water content by 33.5 wt%, which is no more than a half against heat drying system to consume 164 kWh/ton.