A novel cationic waterborne epoxy emulsion for oil filter paper was synthesized. Hydrophilic groups were introduced into a multifunctional bisphenol-A novolac epoxy resin (NEP) by chemical modification, while maintaining the epoxy groups as many as possible, which were neutralized to form the equably water dispersed epoxy resin. The structure of modified NEP in different rate of ring-opening was characterized by Fourier Transform Infrared Spectroscopy (FTIR). The emulsion particle dispersion and micromorphology of waterborne bisphenol-A novolac epoxy resin (WNEP) was detected by granularity measured instrument and TEM. Mechanical properties and microstructure of oil filter papers impregnated by five different waterborne epoxy emulsions were tested and observed by SEM. From the results it can be shown that oil filter paper impregnated by WNEP emulsion has comprehensive properties better than other four commercialized products, exhibiting the best air permeability and improved bursting strength15% higher than that impregnated by poly-styrene-acrylate (PSA) latex.