The invention discloses a preparation method for polyester slices for a heat shrinkable film; with terephthalic acid, modified diol, ethylene glycol and modified dibasic acid as main materials, underthe action of compound auxiliary agents, the polyester slices are obtained by step-by-step beating, low temperature step-by-step esterification, condensation polymerization and grain-sized dicing. Themodified copolyester produced by the method has the advantages of excellent hue, good heat shrinkage, short melting range and small difference between product batches.