The hybrid DC circuit breaker has the advantage of fast fault current interruption with the solid-state switch and low conducting loss with the mechanical switch, which has a broad application foreground in the multi-terminal DC transmission system. The objective of this paper is to determine the mechanism of voltage sharing between the mechanical switch and the IGBT in the hybrid DC circuit breaker during interruption. The mechanism provides evidence to use the lower voltage IGBT in the higher voltage hybrid DC circuit breaker. In the topology researched in this paper, an IGBT and a vacuum interrupter form a series circuit with a parallel capacitor. A hybrid DC circuit breaker prototype is established. The voltage sharing between the IGBT and the mechanical switch are measured with different value of capacitors during experiments. The experiment results illustrate that the mechanism of voltage sharing between the mechanical switch and the IGBT basically likes the transient recovery voltage distribution mechanism of the double-break circuit breaker. Simultaneously, as the parallel capacitor increases, the voltage applied on the IGBT decreases a lot. Hence the IGBT does not need to interrupt high voltage, and the low voltage IGBT can be used, which decreases the cost. At last the practicability of this type hybrid DC circuit breaker is discussed.