This paper is devoted to the simulation of the arc plasma in a simplified low-voltage circuit breaker chamber. Based on a group of coupled governing equations, a three-dimensional (3-D) arc plasma model is built and solved by a modified commercial code. Firstly, this paper presents a solution of the stationary state of the arc plasma and discusses the distribution of some parameters throughout the chamber. Secondly, with the ferromagnetic materials included, the balance of the stationary state is broken and a transient course is calculated. In light of the simulation results, the temperature distribution sequence, the arc motion and the plasma jet are then described and analyzed in detail.