The invention discloses a preparation method for benzoic acid. The employed raw material is toluene, and benzoic acid is prepared by performing oxidation and acid precipitation on toluene and then performing recrystallization and drying. The oxidizing agent is potassium chlorate, the usage amount is 1.2-1.6 times the mass of toluene, oxidation time is 1-2 h, and the reaction temperature is controlled at 95-105 DEG C. In the acid precipitation step, a hydrochloric acid solution with the mass concentration of 30-40% is employed for adjusting the pH value to 1-1.5, and stirring is performed for 30-40 min. In the recrystallization step, a crude product benzoic acid is put in hot water with the amount being 3-6 times the mass of the crude product and with the temperature of 80-95 DEG C, continuous stirring is performed for 15-25 min under the warm-keeping condition, then the temperature is decreased to 2-7 DEG C by using an ice-water mixture, and then standing, crystallization and filtering are performed. The obtained crystal substance is dried by using a drying box, the drying temperature is 55-65 DEG C, and the drying time is 25-35 min. The method is short in technological process, less in by-products and high in product purity.