Polymeric dielectrics with large dielectric constants (ε) and breakdown strength (Eb) coupled with low loss are highly pursued in modern electrical power systems. To synergistically bolster the ε and Eb and restrain the dielectric loss in the barium strontium titanite (BST)/poly(vinylidene fluoride, PVDF), in this research, a crystalline titanium dioxide (TiO2) shell was introduced onto the BST to generate PVDF nanocomposites with high ε and Eb but low loss. The findings show that, in comparison to pure BST/PVDF, the BST@TiO2/PVDF nanocomposites present largely enhanced ε, higher Eb and suppressed dielectric loss. The elevated ε results from the synergistic promotion of inter-particle and intra-particle polarizations in the nanocomposites. The TiO2 shell as a buffer layer availably mitigates the interface mismatch in dielectric parameters between BST and PVDF, thereby heightening the Eb. Additionally, by precisely controlling the TiO2 shell thickness, the best dielectric performances of the nanocomposites can be realized at low filler loadings. The underlying multiple polarization mechanisms are theoretically revealed by analyzing the dielectric data using the Havriliak-Negami equation. The present work provides new insight and paradigm for the design of polymeric dielectrics possessing simultaneously high ε and Eb yet low loss for applications in electrical power systems. Display omitted •The BST@TiO2/PVDF nanocomposites present superior overall dielectric properties than unmodified BST/PVDF.•Fast intra-particle polarization and slow inter-particle polarization are enhanced and can be tuned by the TiO2 shell thickness.•The simulation reveals the BST@TiO2 structure's influence on enhanced permittivity and suppressed loss.•The enhanced polarization in BST@TiO2/PVDF is contributed by a fast intra-particle polarization and a slow inter-particle polarization.