In HVDC transmission systems, the space charge accumulation of polyethylene (PE) insulation is a major problem that threatens the safe and stable operation of cables. In this chapter, nanoparticles and voltage stabilizers are used to inhibit space charge in PE, which has excellent compatibility with PE. To study the thermal, mechanical, and electrical properties of the samples, differential scanning calorimetry (DSC) testing, tensile testing, breakdown, and conductivity property were measured separately. Besides, the space charge behavior based on the PEA method was studied, and the carrier mobility was calculated by the space charge depolarization process. The experimental results indicate that PE modified by graphene oxide (GO) nanoparticles and the voltage stabilizers demonstrate the suppression of space charge accumulation in PE insulation, which has less space charge accumulation than pure PE. The results show that graphene oxide and the preferred stabilizer have broad prospects in HVDC cable applications.