Electroactive materials are of great interest for high performance capacitive behavior due to their relaxed ferroelectric properties. In this work, we studied the dielectric properties of poly(vinylidene fluoride) (PVDF) grafted with polystyrene (PS) by electron beam radiation induced free radical graft copolymerization reaction in solution. The dielectric constant of polystyrene grafted PVDF copolymers reaches about 90 at 100 Hz at room temperature representing more than seven times increment compared with the pristine PVDF matrix. The dielectric loss of 0.005 at 1 KHz can be achieved. Correlation of the dielectric properties with the graft copolymerization reaction mechanism was discussed. This route represents one of the most effective techniques to synthesize potential graft copolymers with desirable dielectric properties in a wide frequency range for energy storage applications.