Insulating material is the basis of advanced power equipment. The performance of insulating material plays an important role in the safe and stable operation of power equipment. The performance of insulating material directly determines the reliability of power equipment. Therefore, it is of great significance to develop high-performance insulating materials such as high insulation and low loss. In this paper, inspired by the one-dimensional nanocell structure, a siloxane-based nanoporous insulating material with nanoporous structure was prepared by sol-gel method. The unique nanoporous structure of the siloxane-based nanoporous insulating material effectively suppresses molecular collision ionization, thereby achieving the purpose of improving the breakdown electric strength. In this paper, the microstructure and thermal stability of the samples were tested by scanning electron microscopy (SEM) and thermal gravimetric analyzer (TGA), respectively. The dielectric properties and insulation properties of siloxane-based nanoporous insulating material and ceramic fiber insulation paper were compared and analyzed by broadband dielectric spectrometer (BDS) and AC/DC breakdown test platform. The results show that the siloxane-based nanoporous insulating material has a relatively uniform nanopore structure and good thermal stability. Compared with ceramic fiber insulation paper, the dielectric properties of siloxane-based nanoporous insulating material are better, and the insulation performance has been greatly improved.