Abstract: The development of high voltage direct current (HVDC) transmission is limited on account of the space charge accumulation in HVDC insulation. The effects of nano SiO₂, micro SiO₂, micro and nano SiO₂ and the preparation process on the space charge behavior in SiO₂/low density polyethylene (LDPE) composites were investigated. The microstructure and crystallization characteristics of different SiO₂/LDPE composites were characterized by SEM, FTIR and DSC. The trap characteristics of SiO₂/LDPE composites were studied using thermally stimulated current (TSC). The space charge behavior in the pure LDPE and SiO₂/LDPE composites were investigated by electro-acoustic pulse (PEA) technique. The results show that the grain size of LDPE is reduced by the introduction of SiO₂, and the crystallinity is increased. The area under TSC curves of SiO₂/LDPE composites increases, the TSC peaks of micro SiO₂/LDPE composites shift to lower temperature, and those of SiO₂/LDPE composites with nano SiO₂ move higher temperature. All SiO₂/LDPE composites exhibit the effect inhibiting space charge to some extent. The preparation process of micro and nano SiO₂/LDPE composite has certain influence on its performance. When the micro and nano SiO₂/LDPE composite is prepared in the form of masterbatch, its performance is closer to the composite corresponding to the inorganic particles added later.