The invention discloses an energy discharging device, a DC power transmission system and an energy discharging method, which are suitable for the field of power transmission of offshore wind power plant. The system comprises an offshore wind power plant, an offshore converter, a DC submarine cable, an energy discharging device, a land converter and an AC main network. Except power grid fault ride-through, DC overcurrent prevention, DC overvoltage prevention and rapid power control, the system also has other properties higher than those of a traditional energy discharging device, large du/dt and di/dt caused by working is eliminated, and energy is smoothly discharged; and meanwhile, a cascaded DC capacitor has a wave smoothing effect, the fluctuation of a DC-side voltage can be reduced under various running modes, and the recovery time after working of the energy discharging device is greatly accelerated.