For a certain product of miniature circuit breakers, a  3D arc  extinguish  chamber model was built and the dynamic characteristic  simulation was calculated.  The  simulation  results  revealed  the movement  rule  of arc in the chamber. Firstly  the  arc  roo ts transferred from  contacts to  arc  runners,  then  the  arc moved along  runners under the effect of the ferromagnetic plate.  Finally, the arc column was divided  into  several pieces by the ferromagnetic splitters.  Several back commutations were observed  in  the process of current interruption.  The  arc  roo t stagnated on the turning point of runner and caused strong ablation of electrodes. The phenomenon was validated by experimental

results. Moreover, the arc voltage and current of simulation were consistent with experimental results.