<p>High dielectric constant and high breakdown strength of nanodielectrics are difficult to achieve simultaneously, which is a challenge that must be faced in the current research, and a single-scale control strategy is difficult to solve the current problem. This study introduced hexafluorobutyl methacrylate (HFBMA) as a crosslinking modifier to prepare HFBMA/PVDF composite films by UV in situ crosslinking strategy. Through the study of multiscale control strategy, it was found that the FTIR results support the occurrence of UV-induced crosslinking, which is likely associated with the formation of a crosslinked network that restricts polymer-chain motion under high electric fields, inhibits the migration of molecular segments, significantly reduces the free-volume defects, and significantly increases the breakdown strength to 587.88&#xa0;MV/m, which is 150% of PVDF (391.33&#xa0;MV/m). The fluorinated side groups in HFBMA may contribute to deeper trapping states and charge-blocking effects because of their strong electronegativity, which is consistent with suppressed carrier migration and reduced space-charge injection, cutting conductivity loss and lowering the leakage current to 5.46 × 10⁻⁷&#xa0;A/cm²—one order of magnitude below that of pure PVDF. As a result, the energy storage density reaches 7.46&#xa0;J/cm³, nearly double the value of PVDF.</p> Graphical abstract <p></p>