<p>With the growing demand for insulating paper with low dielectric loss, high mechanical strength, and excellent thermal stability in advanced electrical equipment, the development of high-performance fiber-based composite insulation materials has attracted increasing attention. In this study, dopamine modification of Kevlar pulp (KP) was employed to enhance the dielectric, mechanical, and thermal properties of KP/softwood pulp (SWP) composite insulating paper. Composite insulating papers with different blending ratios of dopamine-modified Kevlar pulp (MKP) and SWP were prepared, with conventional Kraft paper used for comparison. The effects of dopamine treatment on interfacial structure and on the electrical, mechanical, and thermal properties of the composite papers were systematically investigated. The results show that dopamine modification significantly improves the interfacial adhesion between KP and SWP, suppresses molecular polarization, and reduces both the dielectric constant and dielectric loss. Among the prepared samples, the paper containing 20 wt% MKP and 80 wt% SWP exhibited the best dielectric performance, with a dielectric constant 18.53% lower than that of Kraft paper. In addition, dopamine modification effectively reduced interfacial defects between the two fiber phases, strengthened the fiber network structure, and increased the tensile strength by 38.4% compared with the unmodified composite paper. The dopamine-modified composite paper also demonstrated superior thermal stability and electrical performance. These results indicate that dopamine modification is an effective strategy for fabricating low-dielectric, high-strength composite insulating paper, providing a promising route for the development of high-performance insulating materials for electrical applications.</p>