The invention relates to a synthetic method of a polyether ester block copolymer. The synthetic method includes the steps of: 1) adding raw materials comprising terephthalic acid, 1,4-butanediol and polyether glycol into a reaction kettle, and adding a co-catalyst and an additive, starting stirring, and when the internal temperature is increased to 100-170 DEG C, adding a main catalyst, and continuously increasing the temperature to 210-250 DEG C to perform an esterification reaction to obtain an esterification reaction product; 2) supplying the main catalyst to the esterification reaction product, performing a vacuum poly-condensation process including a low-vacuum poly-condensation and a high-vacuum poly-condensation steps to obtain the polyether ester block copolymer which includes a hard chain segment being polybutylene terephthalate and a soft chain segment being polyether. The copolymer is an elastomer material. The method belongs to continuous polymerization and is stable in the product, inhibits generation of side reactions of the 1,4-butanediol, is increased in esterification positive reaction rate and product yield, and is suitable for large-scale industrial continuous production.