Electric conducting silicon rubber was prepared by filling acetylene carbon black into the rubber. The structures of the conducting rubbers were characterized by SEM and TGA. Then their conducting mechanism was investigated in detail. The results show that the content of carbon black obviously affects mechanical properties of the conducting silicon rubber. But the change of volume resistivity is not obvious when the carbon black content is beyond 45 phr. The structure of “grain/ cluster冶and “chain/ cluster冶formed in the conducting rubber. Therefore, the “electric channels and tunnels冶increased and the volume resistivity decreased. The content of 50 phr is the optimal quantity of thermal resistance for the silicon rubber. With the increase of temperature, the tensile strength of conducting rubbers with 50 phr carbon black decreased gradually. After aging at the temperature of 100益, the conducting property of silicon rubber reduced.