The invention discloses a preparation method of a nano disperse dye. The preparation method of the nano disperse dye comprises the following steps: dissolving the disperse dye in an organic solvent and filtering to remove impurities to obtain an organic solution containing the disperse dye, and recording the organic solution as feed liquid A; dissolving a dispersing agent in water to obtain an aqueous solution containing the dispersing agent, and recording the aqueous solution as feed liquid B; fully mixing and precipitating the feed liquid A and the feed liquid B by adopting a super-gravity rotary packed bed to obtain nano disperse dye slurry; and removing the organic solvent to prepare the nano disperse dye. According to the method, the super-gravity rotary packed bed is adopted, and theparticle size of the prepared nano disperse dye particles is less than or equal to 280 nanometers; particle size distribution is uniform, the dispersity is good, and the PDI value is less than or equal to 0.3; a preparation process is simple, and the reaction time is short; and by the method, the problems of complex disperse dye nanocrystallization process, large product particle size, nonuniformparticle size distribution and the like are solved well, and the nano disperse dye is easy to produce on a large scale.