Abstract: Aiming at the challenge of synergistic improvement between hydrophobicity decay and dielectric performance of electrical equipment insulating materials under complex environments, this study proposes a novel performance regulation method for silicone rubber based on dimethyl silicone oil swelling modification. By swelling high-temperature mixed silicone rubber in 50 cSt silicone oil (swelling ratio 106%), its electrical characteristics and mechanical properties were systematically characterized. Test results indicate that the dielectric constant of the modified material is 3.951, reduced by 6.5%; simultaneously, the surface resistivity decreases by one order of magnitude to 4.32×1014 Ω, while the volume resistivity increases by 32%, forming a unique "surface charge dissipation - bulk insulation enhancement" synergistic mechanism. Mechanical performance tests show a tensile strength of 2.2 MPa, although decreased by 38.9% compared to the control group, it still exceeds the mechanical threshold (1.5 MPa) for electrical equipment insulating materials, and the breakdown strength retention rate reaches 99.8%. The study reveals the differential action of silicone oil molecules on the material"s surface/interface characteristics, holding significant engineering value for improving the external insulation level of power grids in heavy humidity and pollution areas.