The invention discloses polymer waterborne polyester. The polymer waterborne polyester is prepared in the mode that terephthalic acid (PTA), isophthalic acid (IPA), ethylene glycol (BG), diethylene glycol, ternary monomers, a catalyst and other auxiliaries serve as raw materials, and the raw materials and mother liquid are subjected to esterification and condensation polymerization for synthesis. A preparation method of the polymer waterborne polyester includes the steps that firstly, terephthalic acid (PTA), isophthalic acid (IPA), ethylene glycol (BG), diethylene glycol and ternary monomers are made into paste and evenly fed into an esterification kettle through a metering pump, the catalyst is added for an esterification reaction, the auxiliaries are added to monomers generated by the esterification reaction, the mixture is filtered and guided into a condensation polymerization kettle for a condensation polymerization reaction, when a certain process value is reached, the mixture is extruded out through nitrogen, and the transparent polyester product is prepared after cooling, grain-sized dicing, drying and screening. The polymer waterborne polyester replaces traditional acrylic and vinyl acetate products, and urea resin and cyanamide resin which are not environmentally friendly, has a series of advantages of being excellent in adhesive force, high in molecular weight, good in environment friendliness and the like, and can serve as a textile hardening agent to be widely used.