Epoxy resin (EP) has excellent insulation properties, yet the toughness of pure EP is poor, therefore, MWCNTs nanoparticles are added to improve the toughness of EP. However, MWCNTs have excellent conductivity, consequently, organic montmorillonite (OMMT) nanoparticles are attempted to improve the adverse effect of MWCNTs on EP matrix. In this paper, the dielectric and impact properties of three-dimensional composites are characterized and analysed, and the results show that the mechanical properties of matrix are improved by the incorporation of MWCNTs and OMMT nanoparticles, on the other hand, the excessive incorporation of nanoparticles will lead to the increase of dielectric loss and relative permittivity, simultaneously, the increase of electric field frequency will also have a greater impact on the dielectric properties of the composites. In the meantime, the equivalent relationship between the failure caused by voltage breakdown and external loading is studied. Through the relevant research, the relevant properties of the sample can be changed and the damage degree can be reduced under the fixed external voltage.