Polymeric dielectric materials recently attract much attention due to their good comprehensive performances. However, it is still challenging to prepare polymeric dielectric materials with high dielectric constant, low dielectric loss and high breakdown strength. In this work, insulated polyimide (PI) interlayer with nanoscale thickness was coated on the surface of barium titanate (BaTiO3, BT) through the in-situ polymerization and subsequent thermal imidization treatment. The hybrid nanoparticles exhibited the typical 'core-shell'-like structure with strong interfacial interaction between BT and PI. Different from the serious aggregation of BT nanoparticles, the PI@BT nanoparticles exhibited good dispersion in the poly(vinylidene fluoride) (PVDF) composite. There was strong interfacial interaction between PI and PVDF, which resulted in the decrease of crystallinity of the PVDF matrix at relatively high filler content. The flexible PVDF/PI@BT composites exhibited largely enhanced dielectric constant, suppressed dielectric loss and enhanced breakdown strength compared with the common PVDF/BT composites. It was suggested that the intense interfacial polarization at the interface between PI and BT contributed to the largely enhanced dielectric constant while the reduced interfacial polarization at the interface between PI and PVDF contributed to the suppressed dielectric loss. This work demonstrates that the nanoengineering of the interface between BT and PVDF using PI is an alternative way to fabricate the dielectric materials with excellent comprehensive performances.