The invention relates to the field of high polymer material synthesis, in particular to a preparation method of degradable heat-resistant copolyester. The method comprises the following steps: addingterephthalic acid, sebacic acid, 1, 4-butanediol and an esterification catalyst into a reaction kettle for esterification reaction, entering a polycondensation stage after the reaction reaches an esterification end point, adding the polycondensation catalyst, heating while reducing the vacuum degree of a system, reacting until the torque of a motor does not rise to the polycondensation end point,stopping the vacuum of the system, and blowing nitrogen for cooling, then adding polylactic acid, melting, then starting to dropwise add a chain extender hexamethylene diisocyanate, and carrying out chain extension to the maximum value of the motor torque, thus obtaining the block degradable heat-resistant copolyester PBSeT-HDI-PLA. According to the invention, PBSeT is used as a matrix, and the heat resistance of a sample is controllably adjusted by changing the mass ratio of PBSeT to PLA and the content of a chain extender. While the biodegradability is ensured, the thermodynamic property ofthe product is improved, and the mechanical strength of the product is high. The vicat softening point is increased by 16 DEG C compared with the vicat softening point before modification, and the heat resistance is greatly improved.