The invention provides epoxy ester resin capable of being dispersed in water. The epoxy ester resin is prepared from, by weight, 18-22 parts of cardanol, 17-24 parts of epoxy resin, 1.2-1.6 parts of fatty acid, 0.3-0.5 part of phthalic anhydride, 3.2-4.6 parts of polyethylene glycol, 4.3-6 parts of solvent and 47-52 parts of deionized water. The invention further provides a preparing method of theepoxy ester resin capable of being dispersed in water. The epoxy ester resin is low in VOC content, good in hydrolysis resistance stability, rapid in drying, high in hardness and good in corrosion resistance and other performance; cardanol is adopted to replace linoleic acid and dehydrated castor-oil fatty acid in traditional epoxy ester resin in the resin synthesis process, the drying time, hardness, adhesiveness, hydrolysis resistance stability and the like of a paint film are all greatly improved, and cost is greatly reduced; meanwhile, polyethylene glycol is introduced, the epoxy ester resin can be directly dispersed in water, polyatomic acid does not need to be introduced like traditional water-based epoxy ester resin, the water-based aim is achieved through amine neutralization, cost is low, and the process is simple.