Abstract: The SiO₂ particles with diameter of 1 μm, 30 nm and 100 nm were used as additive particles and low-density polyethylene (LDPE) as matrix to prepare the three kinds of SiO₂/LDPE composites. The crystallization behavior and crystallinity of LDPE and three kinds of SiO₂/LDPE composites were analyzed, the relative dielectric constant ε_r and loss factor tanδ changes of each material with frequency were measured, and the conductance current and space charge characteristics of the composites were investigated. The results show that the smaller the particle size is, the smaller the crystal size and grains spacing of the composite materials are. After adding 30 nm SiO₂ particles, the crystallinity increases significantly. The microstructure formed by adding 100 nm SiO₂ particles can effectively limit the chain segment movement, which makes it difficult to establish the polarization of the composites. The addition of large size particles can destroy the original crystal structure, and the new crystal structure can promote the carrier migration. Among the three SiO₂ particles, the addition of SiO₂ particles at 30 nm can effectively inhibit the space charge, while the addition of SiO₂ particles at 100 nm can cause the heterogeneous charge accumulation near the electrode.