The invention provides a method for compounding initiator solution in butyl rubber polymerization reaction, and relates to the technical field of butyl rubber production. The method for compounding the initiator solution in the butyl rubber polymerization reaction comprises the following steps of: a) injecting water into a water container to reach a certain liquid level, and adding a solvent into the container from the bottom of the water container; and b) discharging the saturated water-containing solvent from the top of the water container, and adding into a co-initiator, namely aluminum chloride solution or a polymerization system. The mode of adding saturated water into the solvent is adopted; the addition amount of the water can be accurately controlled by controlling the addition amount of the saturated water-containing solvent; the water is stably added; control over the butyl rubber polymerization reaction can be obviously improved; product quality is improved and stabilized; production efficiency is improved; and equipment is simple, and the method is widely applied.