The invention provides a droop control method and device of a battery. The droop control method comprises the steps of acquiring a DC reference voltage in a no-load condition; determining boundary loss and a droop coefficient of a battery pack; and determining an output voltage of a converter according to the DC reference voltage in the no-load condition and the boundary loss and the droop coefficient of the battery pack. With the droop control method provided by the technical scheme, the boundary loss and the droop coefficient of the battery pack are considered during calculating the output voltage of the converter, automatic control can be achieved only by local information, a communication network is not needed, the attenuation loss characteristic of the battery is considered, the lowest attenuation loss of an energy storage system of the battery is achieved, and the service lifetime of the energy storage system is prolonged.