Dielectric materials are widely used in modern power grids. However, cracking phenomena easily occurs in the using process, and it may lead to partial discharge, electrical treeing, and even system failure. Micro-cracks are difficult to detect, and the replacement of dielectric materials requires a lot of manpower, material resources, and financial resources. Therefore, self-healing materials come into being. The self-healing of dielectric materials can be realized by doping with self-healing microcapsules of which dicyclopentadiene as core material and poly (urea-formaldehyde) (PUF) as wall material. However, PUF microcapsules have insufficient hardness and mechanical properties need to be enhanced. Three sets of models are established by molecular simulation. Each group included a pure PUF model and a PUF model doped with nano-SiO₂. The density, fractional free volume and mechanical properties are analyzed after molecular dynamics calculation. Results show that doping nano-SiO₂ is beneficial to increase the density of PUF materials, reduce the fractional free volume and enhance the mechanical properties. It is found that there are hydrogen bonds interactions between the polar atoms of PUF chain and hydroxyl, as well as O atoms on the surface of nano-SiO₂ by analyzing the interaction mechanism of PUF/SiO₂ interface.