Abstract: A preparation method of original dye of Vat Brown R comprises the following steps: a. after acylation of 1,5-diaminoanthraquinone, 1-amino-5-benzamidoanthraquinone was prepared by acidic hydrolysis; b. 1-benzamido-4-bromoanthraquinone was obtained from 1-aminoanthraquinone by acylation and bromination; c. a condensate of Vat Brown R was obtained by condensation reaction of 1-amino-5-benzamidoanthraquinone and 1-benzamido-4-bromoanthraquinone; d. the original dye of Vat Brown R was obtained from the condensate of Vat Brown R by ring closing reaction and oxidation reaction. The method omits one oxidation step, economizes significant amount of oxidizing agent, and reduces significant amount of waste water, so it is very beneficial to environment protection; and the method also exhibited the advantages of highly increasing product yield and reducing the costs of raw materials to an extent of more than 30%.