The invention provides a high-yield copolyester preparation method. The method comprises the following steps that 1, esterification reaction raw materials of dicarboxylic acid, dihydric alcohol and acatalyst are taken in proportion, the temperature rises to 160 DEG C rapidly, then the temperature rises to 220 DEG C at the rate being 30-60 DEG C/h and is kept until effluent water reaches the theoretical value, and an esterification reaction is completed; 2, thermoplastic polyester is added into a reaction vessel where the esterification reaction is completed, mixing is conducted uniformly, thetemperature rises to 240-260 DEG C, after a reaction system becomes clear and transparent, constant temperature is kept for 10-60 min, the pressure is reduced to be 50-150 Pa, polycondensation is conducted for 1-6 h, and the copolyester is obtained. According to the high-yield copolyester preparation method, less alcohol is consumed, unqualified polyester products or reclaimed materials of wastepolyester can be utilized, reaction is rapid, the yield is high, the production cost is lowered, by-product generation and waste water discharge are reduced, energy conservation, emission reduction and environmental protection are achieved, and the enterprise benefit is increased.