<p>High-temperature dielectric films hold broad prospects in next-generation microelectronics and power systems. However, commercially available dielectric materials for electrostatic energy storage, specifically biaxially oriented polypropylene, suffer from drawbacks such as low energy density, low efficiency, and poor reliability, which limit the application of film capacitors in harsh environments. Herein, a series of naphthalene tetracarboxylic acid dianhydrides were incorporated into polyetherimide (PEI) backbone, thereby modulating the charge transport behavior. Specifically, synergistic regulation of traps and dihedral angles has effectively enhanced the breakdown strength of PEI. At 200 °C, the optimized dielectric film delivers a discharged energy density of 6.00 J cm⁻³ at an efficiency of 90%, and maintains stable performance over 10⁵ charge-discharge cycles at 300 MV m⁻¹. Multilayer stacked film capacitors prepared from the optimized films exhibit remarkable thermal stability and capacitive performance. This work proposes a feasible strategy for developing dielectric films with remarkable energy storage performance, superior thermal stability, and scalable fabrication capability.</p>