NOVELTY - 500-1000 parts mass Terephthalic acid and 200-400 parts mass ethylene glycol are added in reactor, esterification catalyst, polycondensation catalyst and stabilizer are added, and esterification is carried out, to obtain slurry. The slurry is subjected to pre-polycondensation reaction, then subjected to pre-polymerization reaction, 100-300 parts mass reactive phosphorus flame retardant is added, mixed, chain extender ADR and 0.5-50 parts mass hydrolytic aromatic polycarbodiimide are added, copolymerization reaction is performed, and cooled, to obtain polyester material.    USE - Preparation of polyester material used for preparing polyester thin film (all claimed) for backboard of solar cell.    ADVANTAGE - The polyester thin film formed using material has high flame retardance, heat resistance and moisture-proof property.    DETAILED DESCRIPTION - 500-1000 parts mass Terephthalic acid and 200-400 parts mass ethylene glycol are added in a reactor, esterification catalyst, polycondensation catalyst and stabilizer are added, stirred, and esterification is carried out at 245-260 degrees C, to obtain slurry. The temperature of the slurry is raised to 270-280 degrees C, pre-polycondensation reaction is performed, then subjected to pre-polymerization reaction, 100-300 parts mass reactive phosphorus flame retardant is added when the intrinsic viscosity of the slurry reaches 0.2-0.3 g/dl, mixed, 0.5-20 parts mass chain extender ADR and 0.5-50 parts mass hydrolytic aromatic polycarbodiimide are added when the intrinsic viscosity of the polycondensed slurry reaches 0.5-0.65 g/dl, copolymerization reaction is performed, and cooled, to obtain polyester material. INDEPENDENT CLAIMS are included for the following:    (1) polyester thin film, which comprises surface layers (a) and (b), and core layer containing fiber grade polyester chips and masterbatch polyester chips, and further including polyester material. The mass ratio of fiber grade polyester chips, masterbatch polyester chips and polyester material is 100:0-20:1-20; and    (2) preparation of polyester thin film, which involves mixing and melting core layer, surface layer (a) and surface layer (b), carrying out melt extrusion, controlling the temperature at 10-40 degrees C, and stretching along longitude direction.