The novel waterborne epoxy resin emulsion was prepared by the phase inversion technique. The reactive emulsifier, which contains both epoxy group and surface active group, was synthesized by reaction between epoxy resin and a surfactant. The effects of the emulsifier on the stability, particle size of epoxy resin emulsion and its curing property were investigated. Also the film formation and the pot life of the waterborne epoxy system were studied. It was found that at the higher concentration of the emulsifier, the better stability and smaller particle size of the emulsion are obtained, and the film formed is homogeneous, fully cured, therefore it has higher hardness. Film formation of the waterborne epoxy resin system is quite different from solvent based epoxy resin system and pot life of the emulsion should be determined by the gloss change with the time instead of viscosity change.