The invention discloses a preparation method of 3-methyl-2-aminobenzoic acid. The preparation method comprises the steps that 2-chloro-m-xylene is added into an acetic acid solvent for stirring, sodium acetate is added as a catalyst, the temperature is raised to 80-100 DEG C by heating, hydrogen peroxide is dropped for a reaction, after the reaction, 3-methyl-2-chlorobenzoic acid is obtained through rectification under vacuum; the 3-methyl-2-chlorobenzoic acid is added into a DMSO solvent, and catalysts of copper chloride and sodium carbonate are added and heated to 120-140 DEG C, and then ammonia is introduced and heated to 150-160 DEG C for a heat preservation of 3-6 hours, and the 3-methyl-2-aminobenzoic acid is obtained. According to the preparation method, a new design idea is provided for the synthesis of the 3-methyl-2-aminobenzoic acid, the preparation method is simple, operation is easy, the cost is low, and the preparation method is environmentally friendly.