Waterborne saturated polyester (WSP) with high hydroxyl content was prepared through solution polymerization by using stepwise feeding and stage heating methods. The stability of polyester dispersion was enhanced in terms of molecular structure and polymerization process. The conditions of polymerization process, monomer types, and catalyst type were determined. The effects of the ratio of alcohol-to-acid, trimethylolpropane (TMP) content and the feeding method, the content of terminal monomer and branched monomer on the dispersion were investigated. The stability of the self-emulsifying polyester and the water resistance of the film were proved to be excellent. Through transesterification, waterborne unsaturated polyester (WUP) was synthesized by WSP. Polyester-acrylate composite emulsion can be obtained by physical blending or chemical copolymerization of synthetic waterborne polyester. The viscosity of the composite emulsion was improved, and the hardness and water resistance were improved.