The invention relates to a preparation method of high-temperature oil-coal slurry, which comprises the following steps of: (1) conveying pulverized coal from a pulverized coal storage tank into a horizontal solid-liquid mixer through a pulverized coal feeding hole to mix with solvent oil which is sprayed in from a high-temperature solvent tank through a liquid feeding hole, discharging the pulverized coal through a discharging hole of the horizontal solid-liquid mixer and conveying to a coal slurry stirring kettle; (2) further homogenizing the oil-coal slurry in the coal slurry stirring kettle under the action of a stirring paddle; and (3) extracting the oil-coal slurry from the coal slurry stirring kettle through a coal slurry discharging pipeline, wherein one part of the oil-coal slurry is returned to the coal slurry stirring kettle by the coal slurry discharging pipeline, and the rest is conveyed to a downstream liquefaction reaction system by a reaction material conveying pipeline. The method can solve the problem that coal particles of small granularity are hardly and fully dispersed in the solvent oil to form even high-temperature oil-coal slurry, and can be used for rapidly preparing qualified coal slurry and continuously producing coal slurry by a coil liquefaction reaction.