The invention relates to the technical field of cathode electrophoretic paint, particularly an emulsion resin for high-throwing-power cathode electrophoretic paint and a preparation method thereof. On the basis of the solid weight of the emulsion resin, the emulsion resin is composed of (1) 50-70% of modified epoxy resin, (2) 20-40% of closed-terminal isocyanate and (3) 10-20% of imidazolium compounds. The preparation method comprises the following steps: sequentially adding modified epoxy resin, closed-terminal isocyanate, imidazolium compounds and a solvent, heating to 60 DEG C, stirring uniformly, keeping the temperature for 30 minutes, neutralizing by adding an organic acid, stirring at 60 DEG C for 1 hour, slowly adding deionized water in the stirring state, and continuing stirring for 30 minutes after finishing addition, thereby obtaining the resin emulsion. By adopting the scheme, the conductivity of the formed resin emulsion is relatively higher, the throwing power is greater than 20cm, and the voltage resistance of the epoxy resin and the flexibility and shock resistance of the coated film are enhanced.