The invention discloses a direct-current breaker used for a multi-terminal direct-current system and a control method of the direct-current breaker used for the multi-terminal direct-current system. The direct-current breaker comprises a lightning arrester, a main switch branch circuit and auxiliary switch circuits. The main switch branch circuit comprises an isolating switch BRK1, a thyristor T1 and a thyristor T12. The thyristor T1 and the thyristor T12 are connected in an anti-parallel mode and then are connected with the isolating switch BRK1 in series. The auxiliary circuits comprise a first auxiliary switch circuit and a second auxiliary switch circuit which are symmetrical in structure. The first auxiliary switch circuit and the second auxiliary switch circuit are connected in series and then connected with the two ends of the main switch branch circuit in parallel. Each auxiliary switch circuit comprises a thyristor-resistor serial circuit, a capacitor, a resistor and a valve section composed of another thyristor and a diode. Direct current is made to pass a zero to be broken through a method of reverse current injection. The direct-current breaker can be applied to high-voltage large-current occasions, the topological structure of the direct-current breaker is simple, cost is low, breaking is rapid, control is easy, and losses are low.