The invention discloses a synthesis technique of brominated butyl rubber, belonging to the technical field of rubber synthesis. The technique comprises two serial processes comprising bromination of butyl rubber and neutralization of brominated mixture solution. According to the technique, alkane solution of bromine is mixed with alkane solution of butyl rubber in a pipeline reactor, subjected to the bromination, remained for 6s-60s in the subsequent pipeline, introduced into alkali liquor by another pipeline reactor, subjected to the neutralization, and remained for 20s-300s in the subsequent pipeline, then the reaction is finished. The technique has the following characteristics of high reaction speed, short reaction time and exact control, and is suitable for inhibiting the transformation from secondary-bromine substituted principal product to primary-bromine substituted side product; and each index of the obtained product is excellent.