Abstract: The electro-mechanical properties, relation of current and voltage, and electric resistance pre and post-exposed to an electric field of the epoxy-based composites containing N326, conductive, sprayed and N762 carbon black (CB), respectively, are experimentally studied. The influence of the CB content on the three properties mentioned above is also studied. The test results indicate that electro-mechanical properties, relation of current and voltage and electric resistance variation of the CB filled epoxy-based composites are impacted by the CB diameter and content. The composites containing sprayed CB with a diameter of 123nm in the range of 35%~52.5% by mass fraction have good electro-mechanical properties, linear relation between current and voltage, and no resistance variation post-exposed to an electric field. However, the composites containing conductive CB and N326 CB with the diameters of 33nm and 30nm, respectively, do not have obvious regularity in changing the electro-mechanical properties; the relation of current and voltage is nonlinear, and resistance of the composites post-exposed to an electric field decreases dramatically. The composites containing N762 CB with a diameter of 84nm and sprayed CB with a diameter of 123nm in the amount of 26.25% by mass fraction have regular electro-mechanical properties somewhat; the relation of current and voltage is nonlinear and the resistance of the composites post-exposed to an electric field decreases slightly. Furthermore, a DC circuit model based on the experimental research is proposed. The occurrence of electrical breakdown induces the dramatic decrease of electric resistance of the composites post-exposed to an electric field. Finally, the deformation of the epoxy resin layer between two CB particles is employed to interpret the electro-mechanical properties of the CB filled epoxy-based composites.