When a high-current transformer is operated as a generator transformer, the winding current can reach tens of kiloamperes, resulting in increased losses that elevate the winding temperature. The poor thermal conductivity of the insulating paperboard results in localized overheating of the windings, which accelerates the aging of the insulation. In order to improve the thermal conductivity of the insulating paperboard, the insulating paperboard was modified through doping with nano-SiO2. The impact of varying nano-SiO2 concentrations on the thermal conductivity of the nano-SiO2-modified insulating paperboard was then investigated through molecular dynamics simulation, to develop a predictive model of the modified insulating paperboard. A three-dimensional model of a 500 kV power transformer was constructed, and the material parameters of the modified paperboard were incorporated into the simulation analysis of the transformer's magnetic field, flow field, and temperature field. The findings indicate that the thermal conductivity of the material is enhanced by 16.8% at a doping content of 7% of nano-SiO2. Additionally, the maximum temperature on the modified insulating paperboard is 95.1 ℃, which is 2.5 ℃ lower than that of the unmodified paperboard. These results substantiate the exceptional heat dissipation properties of the modified paperboard.