A preparation method of a low-temperature solid-state electrolyte and its application in a low-temperature solid-state supercapacitor, adding acetone to polyvinylidene fluoride-hexafluoropropylene PVDF-HFP, fully dissolving to obtain a transparent viscous solution A, adding electrolyte to the solvent Salt, mix evenly to get electrolyte solution B, mix solutions A and B evenly to get precursor solution C, scrape or cast the precursor solution on a clean and smooth substrate, and get 20-100um low-temperature solid state after natural drying Electrolyte membrane, the solid electrolyte prepared by the present invention has high electrical conductivity at low temperature, and the preparation method is simple and easy, and has wide applicability; the low temperature solid electrolyte is applied to the preparation of low temperature solid supercapacitor, and the prepared solid supercapacitor has a low working temperature To -60°C, it has excellent rate performance, low internal resistance, high energy density and long cycle life at low temperature, which broadens the application of low-temperature solid-state supercapacitors in military or civilian fields.