NOVELTY - Polyester film manufacturing involves adding 200-400 mass% of binary acid, 80-160 mass% of dihydric alcohol, 0.01-0.5 mass% of high branched polyatomic alcohol, 0.01-0.04 mass% of esterification catalyst, 0.04-0.12 mass% of polycondensation catalyst and 0.01-0.06 mass% of stabilizing agent in a slurry making tank. The components are stirred at a speed of 50-100 revolutions per minute (rpm) for 15-30 minutes. The mixture is gradually added in an esterification kettle at 245-260 degrees C.    USE - Method for manufacturing polyester film used in solar battery rear panel film (claimed).    ADVANTAGE - The method enables to manufacture the polyester film having excellent mechanical property, electrical property, humidity resistance, size stability, flame retardant property and water vapor resistant permeability.    DETAILED DESCRIPTION - Polyester film manufacturing involves adding 200-400 mass% of binary acid, 80-160 mass% of dihydric alcohol, 0.01-0.5 mass% of high branched polyatomic alcohol, 0.01-0.04 mass% of esterification catalyst, 0.04-0.12 mass% of polycondensation catalyst and 0.01-0.06 mass% of stabilizing agent in a slurry making tank. The components are stirred at a speed of 50-100 revolutions per minute (rpm) for 15-30 minutes. The mixture is gradually added in an esterification kettle at 245-260 degrees C. Binary acid, a mixture of terephthalic acid and 2,6-naphthalic acid and higher fatty acid or alcohol are also added in the reaction kettle. The reaction mixture is stirred with a speed of 50-80 rpm and then the material is filtered with a filter. Nitrogen is filled to obtain modified polyester resin chip. The modified polyester resin chip and the master batch polyester resin chip are mixed for obtaining polyester film. The dihydric alcohol is ethylene glycol. The polyatomic alcohol is 3-12C polyatomic alcohol having more than 3 active hydroxyl groups. The esterification catalyst for polyester composition is cobalt acetate, sodium acetate or magnesium acetate. The polycondensation catalyst is antimonous oxide. The stabilizing agent is a mixture of trimethyl phosphate, triphenyl phosphate and phosphoric acid. The master batch polyester resin chip is a mixture of polyester master batch chip with barium sulfate, polyester master batch chip with titanium dioxide and polyester master batch chip with silicon dioxide.