To study the impact of high-temperature thermal aging on the space charge characteristics of the silicone elastomer nanocomposites and improve their space charge characteristics after aging, polyhedral oligomeric silsesquioxane (POSS) grafting and organic semiconductor (PCBM) doping are employed to prepare two types of POSS-grafted silicone elastomer nanocomposites, with and without PCBM doping. These nanocomposites were subjected to 500 hours of thermal aging at 250 °C. The space charge and electric field distributions in the nanocomposites were analyzed before and after thermal aging. The results show that before thermal aging, both types of nanocomposites exhibit no space charge accumulation, with uniform internal electric field distribution. After thermal aging, the composites without PCBM doping accumulate significant homo-space charge packet near the electrodes, with significant electric field distortion. In contrast, the PCBM-doped composites accumulate only a small amount of homo-space charges near the electrodes, with lower average charge density and electric field distortion compared to the undoped composites.