5-Aminosalicylic acid is either an important clinical drug or an intermediate in the synthesis of drugs, which can significantly inhibit the inflammation of the intestinal mucosa. Therefore, the research on its synthetic process is of great significance. Here it is reported that the synthetic process of 5-aminosalicylic acid is mainly improved by the “one-pot” strategy. Starting from 2-chlorobenzoic acid, the nitration reaction was carried out by the mixed acids of n (mass fraction 98% sulfuric acid): n (mass fraction of 65% nitric acid) = 6:1, and then nucleophilic substitution reaction with 15% sodium hydroxide obtained the intermediate 5-nitrosalicylic acid, and finally reduction by the reducing agent, iron powder/zinc powder and concentrated hydrochloric acid, gave the final product 5-aminosalicylic acid. The total yield of this synthetic process is 61%, and the structures of intermediate and product were characterized by IR, 1HNMR and MS.