The invention provides a novel preparation method of an insensitive explosive TATB. The method comprises the following steps: 1, with 2,4,6-trinitrotoluene as a raw material, subjecting 2,4,6-trinitrotoluene to reacting with hydrogen and acetic anhydride in sequence to obtain 2,4,6-triacetylaminotoluene; 2, subjecting the obtained 2,4,6-triacetylaminotoluene o oxidation and a decarboxylation reaction to obtain 1,3,5-triacetylaminobenzene; and 3, carrying out nitrification and hydrolysis reactions on the obtained 1,3,5-triacetylaminobenzene to obtain 2,4,6-trinitro-1,3,5-triaminobenzene. According to the invention, the raw material used in the preparation method is the cheap 2,4,6-trinitrotoluene, and used reactants or catalysts are commonly used products in the chemical industry, so the preparation method has characteristics of low cost and usage of simple and easily available raw materials. In addition, the preparation method also has the characteristics of short synthesis steps, simple operation of each step, high yield, high reaction rate, easy separation and collection of intermediate and final products and the like, and is beneficial for realization of mass production of TATB.