Abstract: In this study, the coexistence of high dielectric constant and high breakdown field strength of the polymer-based composite dielectric materials that is simultaneously in possession of a low dielectric loss with application potential were achieved by co-doping with different morphologies of insulating nanosheets and low conductivity spherical particles, which can meet the miniaturization and low energy consumption requirements of high energy storage devices and radio frequency equipment. The polyvinylidene fluoride (PVDF)-based composite dielectric films prepared by the casting method have a filler system composed of self-made magnesium oxide (MgO) nanosheets and titanium dioxide@polyaniline-carbon(BT@C) spherical core-shell particles. The size of the MgO nanosheets is mainly within 300 nm, and the thickness is less than 30 nm. The average diameter of the spherical BT@C core-shell particles with an electrical conductivity of 4.26×10⁻⁵ S/cm is approximately 500 nm. The dielectric constant of the MgO/BT@C/PVDF composite materials with a filling content of 20 wt% has good frequency stability within the wide frequency range of 10² to 10⁶ Hz (range: 4.2 to 6.6), and its dielectric loss is lower than 0.01 over a wide frequency band. Furthermore, the ratio of mass fraction of MgO to BT@C filling content has a significant impact on the dielectric properties of the composite material. In particular, for the composite material with a mass fraction ratio of MgO to BT@C of 2∶3, its dielectric constant is high (6.6, at 10³ Hz) and the frequency stability is excellent (with a decrease of approximately 6%). Meanwhile, the minimum loss value is 0.0052 (at 10⁴ Hz) and the breakdown field strength can reach 344.3 kV/mm and the β value is high (17.8). By taking advantage of the differences in density, physical and chemical properties and morphology among the materials, and through the synergistical regulation of the interface polarization of the filler’s core-shell structure, the multi-parameter balance of the dielectric properties of polar polymer-based composites was achieved. As a result, a PVDF-based composite dielectric with a low loss factor and commercial application potential was obtained.