The present disclosure relates to an initial charging system for a medium-voltage inverter and a method for controlling the system. The initial charging system comprises: a first switch for switching between a medium-voltage inverter and a power supply thereto; a second switch for switching between an output stage of the medium-voltage inverter and an electric motor; a first initial charging unit disposed between and connected to the first switch and the medium-voltage inverter for limiting an initial excitation current to be applied to the phase-shift transformer; and a second initial charging unit disposed between and connected to an input stage of each power cell and the direct current (DC) link capacitor for limiting an initial charging current in the direct current (DC) link capacitor.