Abstract: The rapid development of ultra-high voltage (UHV) transmission technology and increasing demand for high-capacity power transmission have imposed stringent requirements on insulating paper, particularly regarding its electrical performance, mechanical strength, and thermal stability under extreme conditions (e.g., high temperatures and intense electric fields). To address these challenges, this study proposes a synergistic modification strategy combining nano-SiO₂ particle doping with plasma fluorination. We systematically evaluate changes in electrical, mechanical, hydrophobic, and thermal aging properties of insulating paper before and after modification. Surface characterization using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) reveals significant morphological and elemental changes following fluorination. Molecular dynamics (MD) simulations further elucidate the synergistic enhancement mechanism between nanoparticle doping and fluorine- containing groups. Results demonstrate that the combined modification of nano-SiO₂ particles and plasma fluorination effectively restricts charge carrier mobility, significantly improving insulation performance. Compared to unmodified samples, the breakdown strength and volume resistivity of modified insulating paper are increased by 109.2% and 134.9%, respectively. The modified paper surface exhibits abundant grafted fluorine-containing groups, substantially enhancing surface hydrophobicity. Simultaneously, hydrogen bonds formed between fluorine groups and nano-SiO₂ particles strengthened interfacial bridging effects, thereby improving thermal aging resistance.