SiO2 hollow spheres and low relative permittivity insulation paper handsheets composed of these SiO2 hollow spheres with different weight percentages were successfully prepared. Low-content SiO2 hollow spheres were uniformly dispersed in the insulation paper handsheets. The relative permittivity of the immersed oil Kraft-SiO2 hollow sphere handsheets (K-SiO2) initially decreased and then increased with increased amount of SiO2 hollow spheres. K-5% SiO2 possessed the lowest relative permittivity of approximately 1.68 at 50 Hz. The breakdown voltage of the paper-oil-paper composite insulation system increased from 26.4 kV to 30.5 kV with decreased relative permittivity of the paper from 2.55 to 1.68. The relationship between the relative permittivity and electric field strength of typical samples were also calculated.