The present invention provides a method for synthesizing cationic bleach activators via a single-bath reaction, comprising steps of: separately dissolving 4-chloromethylbenoyl chloride and lactam in its respective solvent, adding an acid-binding agent to the lactam solution, next adding dropwisely 4-chloromethylbenoyl chloride solution into the lactam/acid binding-agent solution, and finally adding tertiary amine to the solution above to make a reaction solution, which is further treated with mixing and refluxing. The washed and dried final product is TBLC cationic bleach activator. The method of the present invention greatly simplifies the synthesizing process and lowers the stringency of reaction conditions for preparing cationic bleach activators (TBLC). At the same time, the present method produces TBLC cationic bleach activators with high yields, making it a suitable option for industrial production of these bleach activators.