The invention belongs to the technical field of environment-friendly waterborne coatings, and particularly relates to modified epoxide resin and a preparing method thereof and a high-throwing-power cathode electrophoretic coating with the modified epoxide resin. The modified epoxide resin is prepared from epoxy resin, bisphenol, polyethylene glycol, N,N-dimethyl benzylamine, 4-methyl-2-pentanone,midbody ketimine A, midbody ketimine B, midbody ketimine C, an alcohol ether solvent, propylene glycol methyl ether acetate and polyether amine; corresponding emulsion and color paste are prepared through the modified epoxide resin, and then the emulsion and the color paste are mixed in proportion to prepare the cathode electrophoretic coating. Compared with an existing cathode electrophoretic coating, the throwing power of the cathode electrophoretic coating is remarkably improved, electrophoretic painting of the surface of a workpiece with the complex surface structure can be well met, the surface, the sunken portion, the gap portion and the shielded portion of the painted workpiece are coated with coating layers with the even thickness, the whole corrosion resistance and the like of theworkpiece are effectively improved accordingly, and the application range is wide.