XLPE/nanographene with good dispersibility was prepared via adding six different contents of nanographene. Differential scanning calorimetry was used to measure the crystallinity and the effect of it on the breakdown strength of the polymer was eliminated; the industrial frequency breakdown strength, DC leakage current and flashover voltage of the samples was studied; The mechanical properties of the polymers were evaluated via tensile strength test. Experiments show that the addition graphene nanoparticles can increase the industrial frequency breakdown strength of the polymer by about 27.66%. The DC flash voltage increases with the increase of graphene doping contents. At the same time, the tensile strength was increased by 10.64%. The isothermal depolarization currents were used to calculate the trap levels on the polymer surface. In combination with the dynamic thermomechanical analysis, the mechanism of the effect of six kinds of nanographene doping on the breakdown strength of the polymer was explored from the interfacial molecular binding force. It illustrates that the small content of doping graphene nanoparticles can enhance the intermolecular force of the matrix and reduce the distribution of shallow traps in the polymers.