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With the rapid development of Flexible DC transmission technology accompanied with new sources of electricity in recent years, DC circuit breaker, as the core component of DC system protection and control, has received wide attention. As the power source of the circuit breaker, the operating mechanism’s dynamic characteristics have important influence on the DC breaking capacity. Based on the module prototype of mechanical DC vacuum circuit breaker, this paper established DC breaking experiment platform. Main fracture of the prototype was driven by the repulsion mechanism and the vacuum interrupter used the TMF-AMF compound magnetic field contacts. DC short circuit breaking experiments were carried out based on parameter variables such as the opening speed and contact gap. Through the experiments, the images of the DC arc and the curves of arc voltage were observed, the influence of the dynamic characteristics on the DC vacuum arc shape were investigated. The results were analyzed and, it was showed that with the increase of opening speed, arc ignition time is earlier, the acceleration of opening speed will promote vacuum arc to go diffuse, it means that increase the initial opening speed is beneficial to DC breaking under certain conditions. The results can provide theoretical basis for developing DC special vacuum interrupter and improving the DC breaking capacity of the system.