To improve the dielectric performance of polyvinylidene fluoride (PVDF), BaTiO/MWNTs/PVDF ternary composites were prepared by the solution casting method. The percolation threshold (fraction of MWNTs) has dropped greatly below 0.4 vol %, with the enhancement of dielectric constant and breakdown field. For the BaTiO/MWNTs/PVDF (11.5/0.35/88.15) composite, the dielectric constant is 59, the loss is below 0.055, and the maximum operating electric field is 324 MV/m, so the discharged energy density can be of up to 10.3 J/cm with the efficiency of above 77.2%. The reason of improvement was revealed by the scanning electron microscope images and the X-ray diffraction data. It is found that uniform distribution of filler in the composites and the increase of the β phase of polymers result in the enhancement of polarization and improvement of dielectric constant of PVDF. The third-phase spherical inorganic particles prevent the formation of conductive networks and improve the uniformity of local electric field, so the breakdown strength of composites can be enhanced greatly. Here, this paper provides a method to get the composites with high energy storage density for supercapacitors.