In practical operation, DC field strength and thermal environment can affect the accumulation of space charge in polyethylene cable. And excess space charge can threaten the insulation performance. Although nanocomposites can suppress space charge, the space charge accumulation characteristics after thermal aging still need to be further studied. In this paper, the space charge accumulation behavior in low-density polyethylene (LDPE)/ silica (SiO₂) nanocomposites with different SiO₂ mass concentrations before and after thermal aging was studied by the pulse electro-acoustic method. The results show that thermal aging reduces the electrode injection barrier and generates deep traps and impurities with random distribution, increasing the accumulation of space charge. Many interface regions introduced by nano-SiO₂ generate deep traps with uniform distribution and form interfacial anti-electric field, inhibiting the transport and injection of carriers. Moreover, nanoparticles can improve the stability of materials, thereby enhancing the electrode injection barrier and delaying the thermal aging process. Compared with pure LDPE, LDPE/SiO₂ has the obvious ability to suppress space charge before and after thermal aging.