NOVELTY - Preparing polymer solid electrolyte comprises dissolving 1-2 weight parts of nitrile rubber into 20-30 weight parts of butanone, adding in 20-30 weight parts of methanol so as to precipitate the nitrile rubber; feeding the pure, dried nitrile rubber, lithium perchlorate and epoxy resin to the tetrahydrofuran; storing for 5-10 hours at room temperature, then stirring for 10-30 minutes to obtain uniform and transparent thick solution, casting in polyfluortetraethylene die, vaporizing solvent, and vacuum-drying to obtain a polymer solid electrolyte.    USE - The method is useful for preparing polymer solid electrolyte (claimed).    ADVANTAGE - The electrical conductivity of the polymer solid electrolyte prepared by this invention can reach 1.81x10-4 Siemens/cm at 20 degrees C, which is improved for 2-3 times compared with the pure nitrile rubber/lithium perchlorate polymer electrolyte and equivalent to the electrical conductivity of the polymer electrolyte prepared by compounding the reported nitrile rubber and ionic liquid; properties of the polymer solid electrolyte at 200 degrees C or lower are stable; thus it can meet use requirements of the lithium ion battery.    DETAILED DESCRIPTION - Preparing polymer solid electrolyte comprises dissolving 1-2 weight parts of nitrile rubber into 20-30 weight parts of butanone, adding in 20-30 weight parts of methanol so as to precipitate the nitrile rubber, repeatedly washing the precipitated nitrile rubber with methanol and placing in an oven of 40-80 degrees C to dry for 12-36 hours so as to remove residual solvent to obtain pure and dried nitrile rubber; feeding the pure, dried nitrile rubber, lithium perchlorate and epoxy resin to the tetrahydrofuran, controlling weight ratio of the lithium perchlorate to the nitrile rubber to be 0.3-2.5:1, and weight ratio of the epoxy resin to the nitrile rubber to be 0.15-0.45:1; storing for 5-10 hours at room temperature, then stirring for 10-30 minutes to obtain uniform and transparent thick solution, casting in polyfluortetraethylene die, vaporizing solvent, and vacuum-drying to obtain a polymer solid electrolyte; where content of acrylonitrile in the nitrile rubber is 18-45 wt.%, and Mooney viscosity ML1001+4 is 56-85, and epoxide equivalent weight of the epoxy resin is 185-2000 g/eq.