The invention relates to a switching power unit and a high-voltage direct current circuit breaker; the switch power unit comprises a forward power module and a reverse power module which are connectedin series; each power module is an H bridge module and comprises a first bridge arm, a second bridge arm and a full-control device branch which are connected in parallel; the first bridge arm and thesecond bridge arm are both formed by two uncontrolled device valve groups connected in series in the same direction separately; a full-control device is arranged in each full-control device branch; the series connection point of the two uncontrolled device valve groups of the first bridge arm is the input/output end of the power module; the series connection point of the two uncontrolled device valve groups of the second bridge arm is the output/input end of the power module; and the arrangement directions of the uncontrolled device valve groups in the two power modules are opposite, and thearrangement directions of the full-control devices are opposite. According to the switching power unit, the two power modules are in the form of forward and reverse series connection, so that the length of the current path is effectively shortened, the stray inductance of the branch is reduced, the loss of the power device is further lowered, and the reliability of the valve groups is improved.