The invention relates to a technique for coal conversion wastewater treatment and recycling, and aims at providing a method for preparing a slurry fuel by coal conversion wastewater gradient utilization. The method comprises the following steps of coagulating the coal conversion wastewater, so as to separate three phases of water-containing tar, wastewater and sludge, wherein the tar separated from the water-containing tar is used for preparing emulsifying oil with fluidity, the sludge is filtered and treated to obtain filter residues and sludge slurry with fluidity, and the sludge slurry is used for gasifying or incinerating; blending and mixing the wastewater, pulverized coal, a coal water slurry additive, and the wastewater and residues obtained by separating, so as to prepare the coal water slurry; after the gasified wastewater produced by a gasifying furnace or a boiler is congealed, mixing into the coal conversion wastewater to coagulate, so as to realize the recycling function. The method has the advantages that the three phases of waste tar, waste liquid and sludge in the coal conversion wastewater are utilized in a gradient way, the pollution to the environment by the coal conversion wastewater is decreased, the caloric value of the wastewater is fully utilized, a large amount of slurry preparation water is saved, and the combustion and gasifying property of the coal water slurry is promoted.