The invention discloses a preparation method of thiophenol. The preparation method comprises the following steps of: reacting a chemical compound presented in formula II with ammonium formate / methanoic acid at 160-230 DEG C for 3-10 hours, and removing steam generated during the reaction, wherein the mole ratio of the chemical compound presented in the formula II to the ammonium formate / the methanoic acid is 1:3-6, and in the formula II, R1, R2, R3, R4 and R5 are hydrogen, halogen, hydrocarbyl, alkoxy, hydroxyl, amidogen, amidogen, nitryl, carboxyl, aldehyde group, carbonyl, acylamino, ester group or nitrile group; after reaction, cooling the reaction liquid to 75-85 DEG C, then adding dilute acid to adjust pH to 1.8-2.2; and then rectifying the acid-treated reaction liquid to obtain the thiophenol presented in formula I.