Abstract: The excellent electrical properties of nanomodified insulating oil make it have a wide application prospect. The interface properties between nanoparticles and base fluid are directly related to the electrical properties of nano-modified insulating oil. Therefore, different surface modifiers were used to prepare nano-SiO₂ modified insulating oil in this paper, and the interfacial properties between nano-SiO₂ and insulating oil molecules were explored from the micro level. The experimental results show that the nano-SiO₂ modified insulating oil with the concentration of 0.03 g/L has a higher breakdown performance than pure oil, the increase range is 28.0% and 17.6% respectively and the dissipation factor slightly increases. The breakdown performance of nano-SiO₂ insulating oil modified by APTES is better than that of HMDS. The DFT calculation shows that the interaction energy between APTES modified nano-SiO₂ and alkane is larger than that of HMDS modified nano-SiO₂, and APTES contains amino groups with higher positive potential, which can capture more electrons. Therefore, when electrons are introduced to the interface, more electrons distribute on the APTES modified nano-SiO₂, indicating that the APTES modified nano-SiO₂/alkane interface can capture more free electrons in the oil, thus improving the breakdown performance of nano-SiO₂ insulating oil.