The invention discloses a production process for one-step synthesis of brominated SBS, which belongs to the technical field of brominated SBS production, and comprises the steps of: dissolving SBS with an organic solvent, adding a brominating agent diluted with an organic solvent, the brominating agent adopts bromine The mixture of element and tribromide, the tribromide is trimethylphenylammonium tribromide, add catalyst, the catalyst is tin tetrachloride, the bromination reaction temperature is 10-40°C, and the reaction time is 2 ‑8h; decolorize, wash, and crystallize the feed solution after the above reaction, then pour the crystallized material into a centrifuge, wash with water after centrifugation, filter, and dry to obtain the brominated SBS product. In the present invention, bromine and a small amount of tribromide are added as bromination agents in the production process, and the hydrogen bond substitution reaction is suppressed by adding an appropriate amount of catalyst, so that the addition reaction is the main one, the side reactions are reduced, and the product structure is more stable. The thermal stability of the brominated SBS is improved, and the reaction is a one-step production process, which improves the production efficiency.