The invention discloses a novel method for preparing a cold-resistant and seawater-resistant aqueous filmforming foam extinguishing agent. According to the formula, the cold-resistant and seawater-resistant aqueous filmforming foam extinguishing agent consists of the following raw materials in part by weight: 300 to 400 parts of composite burn resistance agent, 6 to 10 parts of sodium benzoate, 50 to 100 parts of urea, 5 to 9 parts of xanthan gum, 200 to 400 parts of amphoteric hydrocarbon surfactant, 20 to 40 parts of alkyl polyglucoside (APG), 80 to 200 parts of glycol, 30 to 60 parts of butyl cellosolve, 10 to 30 parts of FC115710, 20 to 60 parts of FC120320, 20 to 40 parts of low-molecular-weight fluorinated surfactant, and 20 to 60 parts of buffering agent. The product prepared by the method is low in cost, and suitable for fresh water and seawater; and after the agent and the seawater or the fresh water are mixed in a use mixing ratio, the foam property and the extinguishment performance of the agent change slightly, the expansion rate of foam is high, 25 percent liquid drainage time is long, the foams are stable, the extinguishment speed is high and the burn resistance performance is good.