The invention relates to a high-voltage DC circuit breaker and a through-flow branch for the high-voltage DC circuit breaker. The high-voltage DC circuit breaker comprises one or two DC circuit breaker units connected in series. The DC circuit breaker unit comprises a through-flow branch, a cut-off branch and an energy consumption branch, which are connected in parallel. The through-flow branch is formed by connecting in series an auxiliary commutation module unit and two or more than two parallel mechanical switch units. The auxiliary commutation module unit is formed by one or at least two auxiliary commutation modules connected in series; and the mechanical switch unit is formed by one or at least two mechanical switches connected in series. According to the DC circuit breaker, the two mechanical switch units are connected in parallel in the through-flow branch, so that when system load is too large, the two mechanical switch units are switched in to enable system current to pass through the DC circuit breaker through two paths, and flow capacity of the DC circuit breaker is improved effectively.