The invention relates to a high-voltage DC quick circuit breaker and a power sub-module thereof. The high-voltage DC quick circuit breaker comprises a mechanical isolating switch, a main through-flow branch and a current transfer branch. A circuit which is formed through serially connecting the mechanical isolating switch and the main through-flow branch is parallelly connected with the current transfer branch. The current transfer branch is composed of a plurality of serially connected power sub-modules. Each power sub-module is a mixed sub-module and comprises the components of a pair of power transistors which are serially connected in a forward-and-reverse direction, a pair of power transistors which are parallelly connected in the forward-and-reverse direction, two voltage sharing resistors and a voltage sharing capacitor. Compared with a DC circuit breaker in which a fully controlled device or an H-bridge is used, the high-voltage DC quick circuit breaker is advantageous in that the number of serially connected modules is 1/3-1/2 of that of the previous DC circuit breaker, thereby greatly reducing size of the DC circuit breaker and reducing cost.