The invention relates to a preparation method of 2-bromophenylhydrazine sulfate. The preparation method comprises the following steps of diazotization, reduction, purification and salt formation. In the diazotization and reduction steps, concentrated hydrochloric acid is adopted, so that a reaction liquid is kept to be strong acidic, and the reaction is kept smoothly and completely. In the reduction step, zinc powder and the concentrated hydrochloric acid are used as reducing agents to replace sodium thiosulfate, sodium hydrogen sulfite, stannous chloride and hydrochloric acid and the like, so that good reducing property and high yield are realized, the reaction time is shortened, impurities such as zinc hydroxide and the like generated after the reaction are convenient to remove, and a product is few in impurities and high in purity. In the salt formation step, acetone is used for leaching, so that not only is the purity of the product increased, but also the appearance of the product is ensured. The preparation method is stable and reliable in process, easy to operate, high in product purity (larger than or equal to 99.2% measured by a high performance liquid chromatography), high in yield (larger than or equal to 42%) and capable of completely meeting the requirement of the market for 2-bromophenylhydrazine sulfate.