Abstract: Dielectric elastomers (DE) with compliant electrodes are widely employed in polymer energy transducers. Under high DC electric field, the space charge accumulation and transport process in DE materials will cause the local electric field distortion, which accelerates the insulation aging, damage and failure, further affecting the long-term reliable operation of energy transducer. In this paper, the macroscopic dielectric properties of polydimethylsiloxane (PDMS) and its nanocomposites are characterized by infrared spectroscopy, thermally stimulated depolarization current (TSDC), broadband dielectric spectroscopy, conduction current measurements and breakdown tests. Based on the pulse electroacoustic method (PEA), space charge characteristics of the materials are measured at 20 kV/mm. The results show that the introduction of an appropriate amount of nano silica can reduce the dielectric loss of PDMS at low frequency area, decrease the conductivity and increase the DC breakdown strength. Second, in nanocomposites with higher doping concentration (> 2 phr), the surface-treated particles have better dispersion in PDMS due to mutual repulsion of hydrophobic groups, which still improves breakdown and conductivity performances slowly. In addition, the TSDC and multi-layer barrier structure space charge measurement results show that adding nano silica also leads to an increase in both trap charge amount and trap density, and a reduction of the ionization rate and negative carrier mobility, providing an explanation for the suppression