The invention relates to the technical field of electrophoretic coating, and particularly relates to epoxy acrylic cathode electrophoretic coating resin emulsion and a preparation method thereof. Thepreparation method mainly comprises the following steps: firstly, synthesizing acrylic resin containing a reactive functional group; then, performing chain extension on epoxy resin until the epoxide equivalent is 400-900 with chain extender, and sequentially reacting the epoxy group in the chain-extended epoxy resin sequentially with organic secondary amine and the acrylic resin containing a reactive functional group to prepare epoxy acrylic resin; and mixing the epoxy acrylic resin with full-closed polyisocyanate, neutralizing the mixture with organic acid, and dispersing the mixture with deionized water to prepare the epoxy acrylic cathode electrophoretic coating resin emulsion. The resin emulsion is stable, has low solvent content and can be used as a film forming component of cathode electrophoretic coating; and the film has corrosion resistance, aging resistance and decorating performance, functions of priming coat and finishing coat can achieved by once electrophoretic coating, the coating process can be simplified, and the coating cost can be reduced.