By designing a novel flow-through electrolytic cell, Br2, an unstable and toxic reagent, can be produced in-situ on the near region of a platinum electrode surface by constant current oxidizing KBr in H2SO4medium. At the same time, it was found that a strong CL signal was produced when the basic H2O2solution was injected into the electrolytic cell. Based on this observation, a simple, rapid and selective ECL method for the determination of H2O2was proposed. Factors affecting the determination of H2O2, including the chemical and flow-injection parameters as well as the design of flow-through electrolytic cell, were investigated, and the possible ECL reaction mechanism was also discussed. Under the optimum conditions, the ECL emission intensity was linear with H2O2concentration in the range of 1.0x10−6− 4.0x10−3mol/L and with 3.5x10−7mol/L detection limit.