The preparation of waterborne epoxy resin emulsion was studied，using reverse rotation，the emulsifier was prepared by the reaction of epoxy resin E-51 and polyethylene glycol 4000 under the catalysis of potassium persulfate and mixed with epoxy resin E-51 and deionized water in a certain proportion． Then preparation of waterborne epoxy resin emulsion. The water solubility，stability，structure and particle size distribution of the waterborne epoxy resin emulsion were characterized by infrared spectroscopy，laser particle size analyzer and scanning electron microscopy. Ｒesults show: The optimum condition for the synthesis of emulsifier is n( E-51) ∶ n ( PEG-4000) ∶ n( K2 S2O8 ) = 2. 5∶2. 5∶1，the reaction temperature is 180℃，and the reaction time was 2 h． When the emulsifier content was 20% and the solid content was 60% ，the prepared emulsion has the best water solubility and stability，the particle size distribution of emulsion was in the range of 0. 21 ～ 0. 37 μm.