Preparation method of 2-hydroxy-4-aminobenzoic acid

The invention discloses a preparation method of 2-hydroxy-4-aminobenzoic acid. The preparation method comprises the following steps that 1, m-aminophenol and a sodium alkoxide undergo a reaction in an alcoholic solution at room temperature for 0.8 to 1.2 hours to produce an m-aminophenol sodium salt alcoholic solution; and 2, the m-aminophenol sodium salt alcoholic solution is putted into a high-pressure reactor; carbon dioxide recovery gas is fed into the high-pressure reactor to undergo a reaction for 1 to 5 hours under supercritical conditions of carbon dioxide; after the reaction, the obtained reaction solution is cooled to room temperature and then is filtered; the filtrate is subjected to reduced pressure distillation so that a solvent alcohol is removed and a solid is obtained; the solid is dissolved by water to form a solution; an inorganic acid is added into the solution to adjust a pH value of the solution to a pH value of 6 to 7; and when a solid is separated out, the solution is filtered again to