The invention discloses a hybrid energy storage system direct-current converter based on Buck/Boost circuits and a control method thereof. The hybrid energy storage system direct-current converter consists of a super-capacitor, a storage battery pack, a first inductor, a second inductor, a first MOS tube, a second MOS tube, a third MOS tube, a first diode, a second diode, a third diode, a first capacitor and a second capacitor. The hybrid energy storage system direct-current converter is used for detecting the charge states of the super-capacitor and the storage battery pack and the size of required power or recycled power; and different Buck or Boost circuits can be combined and formed by controlling the turning-on and turning-off of the first MOS tube, the second MOS tube and the third MOS tube, so that a hybrid energy storage system can work in a peak efficiency mode through boosting or bucking. According to the direct-current converter, the operation of the hybrid energy storage system with relatively high efficiency can be realized, meanwhile the number of cycles of the storage battery pack can be effectively reduced, and the service life of the hybrid energy storage system is prolonged.