NOVELTY - Preparing sludge fuel, comprises (i) feeding sludge having moisture content of 80% into synthesis machine from sludge storage bin by a screw pump, mixing, blowing exhaust gas, pumping gas from the work site of the synthesis machine, and burning harmful materials formed on one side of hot air furnace; and (ii) drying sludge fuel, evaporating, separating harmless water vapor emissions, adding lime, sodium hydroxide or magnesium oxide as quenching and tempering agent, and adding wooden meal and straw stick, and stacking or storing varieties of fuels into a stockyard.    USE - The method is useful for preparing sludge fuel (claimed).    ADVANTAGE - The method saves energy; is environmental friendly, and economical; has easy operation procedure; and recycles resources, so as to meet the meet specified standards of harmless components.    DETAILED DESCRIPTION - Preparing sludge fuel, comprises (i) feeding sludge having moisture content of 80% into synthesis machine from sludge storage bin by a screw pump, and uniformly mixing the materials weighed based on the certain measurement, where the bottom part of the synthesis machine is provided with an electronic weighing device which can automatically weight each materials added in sequential manner, and conveying the materials into a hot air drying machine which is provided with a heat exchange energy saving device and a water bath cyclone de-dusting device, and then blowing exhaust gas from a hot air furnace into a storage bin by an air suction port, and pumping gas from the work site of the synthesis machine, removing exhaust gas from the hot air drying machine by heat exchange energy saving device, and burning harmful materials formed on one side of hot air furnace, and conveying the high-temperature hot air produced into the hot air furnace; and (ii) drying sludge fuel by adding into a hot air dryer, until the moisture content of the bulk materials reaches 20%, sludge fuel produced in hot air furnace is used as synthetic fuel, evaporating moisture content from waste heat produced in an exhaust port, and discharging heat from the water bath cyclone de-dusting device, and conveying into heat exchange energy saving device, and separating harmless water vapor emissions, and completely adding the components into electrical automatic control cabinet, and controlling moisture and temperature by automatic measurement control-operation system, and adding lime, sodium hydroxide or magnesium oxide as quenching and tempering agent, and adding wooden meal, straw stick, powder coal (coke powder) or cooking oil into a combustion improver, and stacking the materials or storing varieties of fuels formed by conveying from the conveyor into a stockyard.