Abstract: Conductive ABS resin composites filled with general pitch-based carbon fibers were fabricated by hot-press moulding after raw materials were preblended through a single screw extruder. The composite resistivity decreases with fibers content going up. And the electrical current displays non-linear dependence on the external voltage acted on composites and the resistance of composites varies down with the raise of voltage, which implies that the composites don't meet Ohm's Law. When fibers fraction increases, the linearity between current and voltage goes up correspondingly. For the sample containing fillers of 40 wt%, its resistance remains constant and it satisfies Ohm's Law very well. It is interesting that the high voltage can result in the permanent reduction of composite resistance. And the voltage, which makes the permanent reduction of composites resistance, goes up with the increase of fillers loading. Moreover, the linearity of current and voltage rises after composites were treated by high voltage. All these phenomena can be explained by quantum tunneling model the results of this paper provide a new method for improving the conductivity and stability to varied voltage of composites.