The invention belongs to the technical field of dyes, and particularly relates to a preparation method of a cationic
blue dye. According to the invention, a compound II is used as a diazonium component and a compound I is used as a
coupling component for synthesizing the cationic
blue dye for the first time; and the method has the advantages of simple process, environmental friendliness, high product purity, high yield and the like. The results of multiple production experiments with scales not below
pilot tests show that
mother liquor (such as
mother liquor in steps 2, 3 and 4) in the reaction process can be cyclically used 6-8 times without treatment, so the amount of high-salt, high-COD and high-chroma
wastewater is greatly reduced, a
working environment is effectively improved while product yield is further increased and reaction
reagent cost is saved, and the product still keeps high purity; and thus, product quality is guaranteed, production cost is reduced, and obvious economicbenefits,
social benefits and environmental benefits are produced.