The invention discloses a large-sized energy storage power battery stack fire extinguishing system and a fire extinguishing method thereof and belongs to the field of large-sized energy storage powerbattery stack fire extinguishing. The large-sized energy storage power battery stack fire extinguishing system comprises a battery stack fire monitoring alarm and control module, a water pump module,a thermosetting gel additive, a high boiling point halogenated hydrocarbon additive, an additive mixing module, a zone control module and a fire extinguishing nozzle; an output end of the additive mixing module is connected with an input end of the zone control module; and an input end of the fire extinguishing nozzle is connected with an output end of the zone control module. According to the large-sized energy storage power battery stack fire extinguishing system, an adopted high boiling point halogenated hydrocarbon gas fire extinguishing agent is clean and environmentally friendly and hasno harm to an atmospheric ozone layer. According to the large-sized energy storage power battery stack fire extinguishing system, as the thermosetting gel additive is dissolved in the water at the room temperature to form a thermosetting gel additive aqueous solution, and the thermosetting gel additive generates a gelatination phenomenon to cover and coat the surface of an inflamer in the form ofgels; and therefore, long-distance cooling is realized to inhibit battery chemical combustion reaction so as to stop secondary out-of-control of a battery.