The invention relates to a winter anti-freezing method for a firefighting water storage tank. The head end of a heating coiled pipe inside the firefighting water storage tank is connected with heating steam, and the tail end of the heating coiled pipe is connected with a section of vertical discharging pipe. The vertical discharging pipe extends out of the top of the storage tank and then turns downwards back into the storage tank, and a steam trap is installed at the tail end of the vertical discharging pipe. When water inside the firefighting water storage tank needs to be heated, a steam valve is opened firstly, the steam enters the heating coiled pipe through the valve, and passes through the surface of the heating coiled pipe to be subjected to heat exchange with the firefighting water in the firefighting water storage tank. Condensate water obtained through condensation of the steam in the heating coiled pipe falls into the firefighting water in the firefighting water storage tank through the steam trap of the vertical discharging pipe. The steam condensate water with high temperature and heat energy returns to the firefighting water storage tank and is used for indirect supplementation and heating of the firefighting water, the supplementation amount of the firefighting water is reduced, water resources are saved, energy waste is avoided, and the remarkable energy-saving effect is realized. The steam condensate water does not enter a sewage treatment system any more, so that the sewage treatment burden is relieved.