NOVELTY - Synthesis of bromo-chloro-dimethyl hydantoin involves adding dimethyl hydantoin, sodium bromide, sodium hypochlorite stabilizing agent and deionized water to reactor, adding sodium hypochlorite solution to reaction mixture to form pale yellow precipitate, separating reaction mixture and generated precipitate to obtain high purity bromo-chloro-dimethyl hydantoin product and adding in mother liquor after the separation of added dimethyl hydantoin, sodium bromide and stabilizing agent to recycle mother liquor.    USE - Synthesis of bromo-chloro-dimethyl hydantoin (claimed).    ADVANTAGE - The stabilizing agent provided prevents the decomposition of sodium hypochlorite from deep oxidation, so that synthesis yield is increased and production cost is reduced. The volatile and highly-corrosive chemical materials are unused, so that the reaction process is controlled easily. The production process is safe and environmentally-friendly.    DETAILED DESCRIPTION - Synthesis of bromo-chloro-dimethyl hydantoin involves adding dimethyl hydantoin, sodium bromide, sodium hypochlorite, stabilizing agent and deionized water to reactor, stirring the reaction mixture and cooling in ice salt bath to 5-25 degrees C, adding sodium hypochlorite solution slowly, until the color of reaction liquid changes from colorless to yellow, and gradually turns white, , adding sodium hypochlorite solution to reaction mixture slowly, adding hydrochloric acid and alkali salt , forming bromo-chloro-dimethyl hydantoin as pale yellow precipitate, controlling chlorination temperature to 5-25 degrees C, when the precipitation is increased with non-evolution of gas, when the chlorination reaction is completed with molar ratio of dimethyl hydantoin, sodium bromide, stabilizing agent, hydrochloric acid, sodium hypochlorite and deionized water as 1:0.95-1.05:0.05-0.5:2-2.5:2-2.5:10-50, separating the reaction mixture and generated precipitate by filtration, washing the precipitate with deionized water and drying to obtain high purity bromo-chloro-dimethyl hydantoin product, and adding the product in mother liquor after the separation of added dimethyl hydantoin and sodium bromide and stabilizing agent to recycle the mother liquor in next batch synthesis.