The coaxial measurement system of electrical conductivity for the detonation products was improved. The average electrical conductivities of cast TNT mixed with RDX, Al, KCl were studied, and the curves of maximal average electrical conductivity vs RDX fraction α in cast TNT/RDX compositions were obtained. Results show that the maximal average electrical conductivity decreases with the increasing of RDX fraction α in cast TNT/RDX compositions. The electrical conductivity of aluminized TNT is obviously higher than that of TNT, and the maximal average electrical conductivity of TNT 95/Al 5 (density 1.662 g·cm^-3) is over 4 times of cast TNT (density 1.618 g·cm^-3). Also the electrical conductivity of TNT/RDX increases when KCl is mixed in TNT/RDX compositions.