To identify a nanocomposite material capable of mitigating surface charge accumulation issues in silicone rubber composite insulators, this paper investigated the surface charge dissipation characteristics of micron-sized Al2O3/silicone rubber composites with different weight percentages under positive dc voltage. Furthermore, this paper investigated the influence of the uncharged and charged silicone rubber on the surface flashover voltage under positive dc voltage. The result show that the addition of micron-sized Al2O3 particles effectively ameliorates the severity of surface charge accumulation. In comparison to pure silicone rubber, the reduction in maximum surface charge density and average surface charge density of different weight percentage Al2O3/silicone rubber composites ranges from 18.60% to 50.60% and from 33.26% to 57.53%, respectively. When there is no surface charge on the silicone rubber surface, the addition of micron-sized Al2O3 particles at different weight percentages results in a decrease in positive dc surface flashover voltage. Conversely, when a positive surface charge is applied to the silicone rubber surface, the greatest reduction in positive dc surface flashover voltage occurs in pure silicone rubber. Furthermore, the positive DC flashover voltage of pure silicone rubber can recover to 86.53% of its value without applied surface charge at a decay time of 60 minutes. In contrast, the addition of micron-sized Al2O3 particles at different weight percentages diminishes the impact of surface charge on the surface flashover voltage, allowing it to recover to 92.03% to 94.18% of its value without applied surface charge.