The invention discloses a capacitive buffer type mixed high-voltage direct current circuit breaker and a control method thereof. The circuit breaker comprises a mechanical switch unit, a current conversion unit, a capacitive buffer unit and a mechanical switch energy supply unit, wherein the mechanical switch unit is formed by connecting at least one mechanical switch sub-unit in series; the mechanical switch sub-unit is formed by connecting a mechanical switch, a voltage sharing module and an energy-absorbing voltage-limiting module in parallel; the current conversion unit is formed by connecting a power electronic switch module and a voltage-limiting module in parallel; the power electronic switch module comprises at least one power electronic device; the capacitive buffer unit consists of capacitor banks and provides a current conversion buffer branch for fault current; the mechanical switch energy supply unit supplies electric energy to the mechanical switch, and the quickness and the coordination of the motion are ensured. The capacitive buffer type mixed high-voltage direct current circuit breaker and the control method thereof, provided by the invention, have the advantages that the capacitive buffer type mixed high-voltage direct current circuit breaker is simple in structure, convenient to control, high in speed, high in reliability, high in galvanization voltage resistance level, small in size and low in cost.