Disclosed is an anionic, self-emulsified aqueous epoxy resin dispersion prepared through the semi-esterification reaction between a dicarboxylic acid anhydride and the secondary hydroxy group of an epoxy resin, followed by neutralization of the carboxylic acid thus introduced into the epoxy resin with a tertiary amine and then adding only water, without the need of any emulsifier, to the resulting hydrophilic amine salt of the carboxylic acid. The stable aqueous epoxy resin contains both carboxyl and epoxy groups which are reactive functional groups. Also disclosed is a "single-pack" curable aqueous epoxy resin system "cross-linkable" at normal temperature prepared by adding a compound containing polyaziridine as a cross-linking agent into the aqueous epoxy resin dispersion. Upon drying, the liberated carboxyl group in the aqueous epoxy resin reacts with the polyaziridine to form an amino ester via a ring opening reaction. The amino group further reacts with the epoxy group of the epoxy resin to run another cross linking reaction to complete a "double cross-linking". The novel double cross-linking process according to the present invention also can be used in a hybrid resin obtained by blending the aqueous epoxy resin dispersion and other carboxyl- or epoxy-containing aqueous resins, to cure the hybrid resin.