Dielectric polymers have been extensively employed in renewable energy conversion, hybrid electric vehicle, and high voltage direct current transmission systems, owing to their excellent electrical insulation, processability, and self-healing capability. However, the challenge lies in their relatively low dielectric constant (εr) and limited discharge energy density (Ue), which hinder the advancement of integrated power modules. Despite numerous efforts aimed at enhancing Ue, the fabrication of scalable dielectric film with both enhanced Ue and high charge–discharge efficiency (η) remains a major obstacle. Herein, the polypropylene-based films with BaTiO3@PP-g-MAH (BTO@PP-g-MAH) core–shell nanoparticles are prepared through a continuous melt extrusion process. The resulting nanocomposite film, incorporated with 5 wt% BTO@PP-g-MAH, exhibits an impressive Ue of 5.15 J cm−3 and achieves a high η of 93.2 % at 433 MV m−1, along with excellent cycle dielectric stability. Such enhancements in εr and Ue are ascribed to the improved interfacial polarization facilitated by BaTiO3 nanoparticles and the enhanced interface binding achieved through the PP-g-MAH shell layers. Furthermore, the enhancement of electric breakdown strength (Eb) is comprehensively investigated based on electrical breakdown mechanism and electromechanical breakdown model. This study demonstrates a novel strategy to prepare nanocomposite dielectric films that are compatible with commercial capacitor fabrication process.