Abstract: With the expansion of the interconnection scale of the power system，the impedance ratio of the

power grid increased gradually，thereby the breaking capacity of the circuit breaker was affected by the increasing

attenuation time constant of the DC component of the short-circuit current .At present，the periodic component of the short-circuit point in the check of the breaking capacity of the circuit breaker is only considered in the actual power grid，instead of the influence of the DC component and the branch short-circuit current. Firstly，the reduction methods for checking the breaking capacity of the circuit breaker by considering the DC component in the checking of various circuit breakers were compared and analyzed. Then，combined with the calculation method of the DC component of the branch short-circuit current，a method for checking the breaking capacity of the circuit breaker was formulated considering the sequence of the circuit breaker's action. Finally，the breaking capacity of the circuit breaker was checked by calculating the periodic component and DC component of the short-circuit current on the connection branch of the fault point in combination with the power grid in a certain area.The calculation example shows that the influence of the DC component attenuation time constant on the breaking capacity can be fully considered by the reduction coefficient method，which provides a reference for the planning and operation of the power grid and the selection of equipment.

      Key words: short-circuit current；DC component；breaking capacity of the circuit breaker；branch current