Abstract: The influences of stirring time and surface modification of carbon black (CB) on the resistivity and electromechanical properties of CB filled epoxy matrix composites were experimentally studied. The test results indicate that the dispersion of CB in the epoxy can be improved with the increase of stirring time，which is at tributed to the fact that some conductive chains in the epoxy formed by CB are broken up when the stirring time increases and thus the resistivity of composites is improved. Consequently，the variation coefficient of resistivity and the fractional change of resistance versus strain between the specimens prepared at the same time are decreased. But the dispersion of CB in epoxy cannot be further improved when the stirring time becomes longer and the CB particles dispersed in epoxy are still in formation of big agglomerations. The dispersion of CB particles in epoxy is improved further after the surface of CB particles is modified by silane coupling agent. The CB particles modified by silane coupling agent are dispersed in epoxy in formation of little agglomerations and even single particles，so the epoxy gaps between CB agglomerations become thinner and the resistivity and the fractional change of resistance versus strain of the composites decrease accordingly.