Based on the original structure Of the miniature circuit breaker (MCB），an improvement method to quicken arc extinction is present in this paper. An arc-guiding Plate is added to the magnet yoke in arc extinguish chamber. The arc can be more quickly led to the arc extinguish chamber with the improvement when the breaking arc is happened. The damage of the two contacts is reduced，and the electric energy is released’ The comparing experiment are done for two situations Of primary and improved prototypes. The wave forms Of the current and voltage are recorded. The validity Of the improvement method has been confirmed with the experiment. Meanwhile，a measurement method to calculate the quenching time is put forward by using the envelope Of the voltage. The advantage Of this improvement is proved. Keywords：miniature circuit breaker(MCB）；arc-guiding Plate；arc extinction；envelope Of the voltage