NOVELTY - Solid state composite polymer electrolyte comprises polyethyleneimine, polyethylene oxide, citric acid, lithium salt and filler. The mass ratio of the polyethyleneimine and the lithium salt, the polyethylene oxide and lithium salt, the citric acid and lithium salt, and the filler and lithium salt is 0.1-0.5:1, 1.5-3:1, 0.05-0.2:1, and 0.1-0.5:1, respectively. The filler is lithium nickel cobalt aluminum oxide-containing compound.    USE - Solid state composite polymer electrolyte for use in lithium-ion rechargeable battery.    ADVANTAGE - The electrical conductivity of the composite polymer electrolyte is raised (preferably 8x 10-3 S/cm) and reduced viscosity coefficient. It has improved machinability.    DETAILED DESCRIPTION - Solid state composite polymer electrolyte comprises polyethyleneimine, polyethylene oxide, citric acid, lithium salt and filler. The mass ratio of the polyethyleneimine and the lithium salt is 0.1-0.5:1. The mass ratio of the polyethylene oxide and lithium salt is 1.5-3:1. The mass ratio of the citric acid and lithium salt is 0.05-0.2:1. The mass ratio of the filler and lithium salt is 0.1-0.5:1. The filler is LiNi1-x-yCoxAlyO2.    x+y=less than 1;    x=greater than 0 but less than 1;or    y=greater than 0 but less than 1.    An INDEPENDENT CLAIM is included for a method for preparing the solid state composite polymer electrolyte comprising:    (A) adding the polyethyleneimine, citric acid, and lithium salt into the organic solvent and having the ultrasonic dispersion operation for 15-30 minutes, magnetic stirring for 2-4 hours to obtain uniform solution, adding the polyethylene oxide into the solution and blending;    (B) mixing the filler with the organic solvent, having the ultrasonic dispersion operation or blending for 15-30 minutes, magnetic stirring for 16-24 hours and holding for 0.5-1 hour; and    (C) mixing the mixture in step (A) and the mixture in step (B) and pouring in the mold and vacuum drying for 24-36 hours at 50 degrees C to obtain the composite polymer electrolyte.    The organic solvent and the lithium salt ratio in step (A) is 10-50 ml:1 g.