In order to effectively store energy and better improve the dielectric properties of polyvinylidene fluoride (PVDF), this article uses hydrothermal synthesis to prepare spherical Na0.5Bi0.5TiO3 (NBT) particles, and the obtained KH550-NBT was filled into PVDF matrix. The effects of NBT nanoparticles content on the microstructure, electrical properties and mechanical properties of NBT/PVDF composites were studied. The results show that the spherical particles are about 150 nm in diameter, and when the addition amount is 15 wt%, NBT/PVDF has low dielectric loss (0.015), energy storage density (2.58 J/cm3) is 23.4% higher than that of pure PVDF. The breakdown strength is also maintained at 208 kV/mm. This can be explained as the synergistic enhancement of polarization and breakdown field strength under the action of fillers, thereby improving the energy storage performance. At the same time, according to the dynamic mechanical analysis, NBT also makes the storage modulus (1481.97 MPa) higher than the original PVDF (976.65 MPa), improve the mechanical properties. This also provides a new idea for the further development of flexible energy storage capacitor.