The invention provides a fire extinguishing device. The fire extinguishing device comprises a fire extinguishing agent storage tank, a fire extinguishing agent spray head, a smoke detecting alarm, a gas detector, a data processor and a controller. According to the fire extinguishing device provided by the invention, a real-time smoke concentration, gas compositions and concentration data in a battery box are obtained by the smoke detecting alarm and the gas detector; fires are classified into levels trough the data processor according to each piece of received data; and for different fire levels and the location of a battery module where a fire occurs, after the fire extinguishing agent spray head is positioned above the battery module where the fire occurs, the flow regulator is controlled by the controller to adjust a release flow and a release time of the fire extinguishing agent to determine an optimum fire extinguishing agent release flow and an optimum configuration amount. According to the fire extinguishing device, rapid fire extinguishing is realized to greatly improve the fire extinguishing efficiency, and the use of the fire extinguishing agent is saved to the greatest extent to decrease the influences, on battery energy storage systems, of the fires.