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Meta-aramid insulating paper, comprising precipitated fibers as the matrix and chopped fibers as the reinforcing skeleton, exhibits tremendous potential as a next-generation insulating material in high-voltage systems. However, its insulating performance is hampered by severe interface defects, thus limiting its industrial applications. To address this issue, an interface modification method is proposed based on the tunable electrical polarity of chopped fibers, achieved through a practical PDDA treatment, which converts the originally negative potentials of chopped fibers in pulp water to a positive state. As a result, a compact and cross-connected paper structure is formed, wherein the precipitated fibers and chopped fibers exhibit opposite electrical polarities, promoting strong intermolecular attraction and significantly reducing interface defects. We systematically investigate the electrical insulation and mechanical tensile properties of the modified papers, demonstrating remarkable improvements of up to 31% for breakdown strength and 35% for tensile strength. In addition, molecular simulations reveal enhanced compatibility at the fiber interface, driven by the modification of electrical polarity. This study presents an effective approach for designing high-performance meta-aramid paper, while also opening up possibilities for interface modification in various fiber-reinforced composite materials.