The invention specifically relates to a synthetic method for a precursor of an anthraquinone reactive disperse dye used in supercritical CO2, which belongs to the technical field of dyes. According to the method, 1-chloroanthraquinone and 2,5-diaminotoluene sulfate are used as raw materials, K2CO3 is used as an acid-binding agent, and CuI is used as a reaction catalyst, a heating reflux reaction is carried out at 80 to 140 DEG C for 6 to 14 h under the protection of nitrogen; and after completion of the reaction, post-treatment is carried out so as to obtain solid powder of the dye precursor. The method has the advantages of a low usage amount of the catalyst, mild reaction conditions, high yield and low cost, and the obtained precursor has good applicability; and the method is applicable to synthesis of the anthraquinone reactive disperse dye used in supercritical CO2 and to synthesis of reactive disperse dyes used in conventional water-bath dyeing.