A multiblock epoxy emulsifier with bifunctional group (Hydroxyl and Carboxyl) was synthesized by a series of raw materials, including epoxy resin (E-44), trimellitic anhydride (TMA) and polyethylene glycol (PEG4000) in the presence of the catalyst boron trifluoride etherate. Then waterborne epoxy emulsion was prepared by phase inversion method with the above emulsifier. The chemical structure of emulsifier was characterized by FTIR、1HNMR and GPC. The effects of the amount of catalyst, reaction temperature and time on the esterification epoxy conversion rate in the emulsifier synthesis process were studied. Simultaneously, the effects of the amount of emulsifier and emulsifying temperature on Emulsion stability were explored. The optimum conditions of synthesis emulsifier: catalyst dosage was 0.36 % (the total reactant mass), esterification reaction time was 2 h and temperature was 70 ℃, esterification rate reached 96.6 %. Epoxy ring-opening reaction time was 5 h and temperature was 95 ℃, ethylene conversion reached 94.2 %. Moreover, the emulsion with small average particle size (about 312 nm) and good stability was obtained when emulsifiers dosage was 15 % (the mass of E-44) and temperature was 60 ℃.