Embodiments of this application provide an energy storage system and a black start method. The energy storage system includes a black start controller, a battery module, a first converter, and a system control unit. The black start controller outputs a black start signal, the battery module generates an output voltage based on the black start signal, and the first converter supplies power to the system control unit based on the black start signal and the output voltage of the battery module, to enable the system control unit to implement black start of the energy storage system based on the black start signal.