<p>Polymer-based dielectric materials with high energy density and thermal stability have become an urgent necessity in modern electric/electronic industry. Among them, polyimide (PI)-based materials have drawn ever-increasing attention in the fabrication of polymer dielectrics due to their high temperature resistance and chemical inertness. Nevertheless, the inherent low dielectric constant and limited charge-discharge energy density of the PI materials severely restricted their applications in dielectric film capacitors. Although the dielectric and energy storage performances of polyimides can be easily optimized by incorporating ferroelectric or conductive fillers, batch-to-batch inconsistency and progressive physical deterioration remain serious issues in their applications. Herein, focusing on structure design and modulation, hyperbranched polyimides with different dianhydride monomers and branching degrees were prepared. The effects of chain packing density with polar groups on the dielectric and energy storage performances of different PI materials were systematically studied by both experimentation and molecular simulation. Results showed that the dielectric properties exhibit a significant correlation between monomers’ electrical distribution and their packing density in polymer systems. Moreover, the molecular simulation results further elucidated the underlying mechanism. Therefore, we speculate that this work establishes a solid foundation for designing and fabricating polymer-based dielectric materials with high dielectric and energy storage performances at the molecular level.</p>