Abstract: During the fault breaking process, the metal vapor arc plasma in the vacuum interrupter with a transverse magnetic field moves at high speed along the contact surface, and the evolution of the arc dynamic behavior directly affects the breaking performance of the vacuum circuit breaker. In this paper, in order to study the action of magnetic blowing force on the arc during the breaking process, and to analyze the influence of the motion characteristics of the operating mechanism on the breaking performance, combing the operating mechanism characteristic of the 12 kV/1250 A/25 kA vacuum circuit breaker, a three-dimensional finite element transverse magnetic field model is established. The research results indicate that the rotational speed of the arc root on the contact surface can be increased by improving the speed characteristics of the mechanism; however, the magnetic field is correspondingly weakened. In addition, by analyzing the effect of contact structure parameters on the force exerted on the arc, it can be obtained that, moving the starting point of the slot towards the outside of the contact or reducing the slot width is beneficial for the arc to cross the slot, and the stagnation time of the arc on the contact surface can be reduced to improve the breaking capacity of the vacuum circuit breaker.