To the optimization design of molded case circuitbreakers (MCCBs), it is important and necessary to simulatethe interruption process and analyze the characteristics. A setof differential equations can describe the interactive coupledphenomena of electric circuit, electromagnetic field and mechanismmotion system in MCCB. First, with virtual prototypingtechnology, the simulation model for the operation mechanismof MCCB can be built, and experiments have been carried outto verify its validity. Then, with the existence of electrodynamicrepulsion force, the interruption process of the MCCB has beeninvestigated with the influence of arc voltage, closing phase angle,prospective current, mechanism starting motion time and blowopen force. It demonstrates the proposed method is effective andis capable of evaluating the new design of MCCB products.