A preparation method of vinyl ester resin for optimizing heat-release during curing includes: (A) providing a vinyl ester, a solvent and a phase change material to perform mixture; (B) performing a heating process to remove the solvent, so as to obtain a vinyl ester resin containing the phase change material. Thereby, the organic PCM material with high heat absorption and good resin affinity can be used as the temperature control agent of the vinyl ester resin during the curing process for avoiding the defects such as bubbles and cracks being generated in the vinyl ester resin.