The scheme of planar measurment method of electrical conductivity in the shock initiation process for condensed explosives was established. The electrical conductivities of TNT under different initial shock loading and RHT-906 explosive were studied with the method. The effect of initiation pressure on the electrical conductivity was analyzed. The results show that the highest electrical conductivity decreases with the decreasing of initiation pressure and it decreases when RDX is added in TNT. The chemical reaction time of TNT explosive detonating of experiment No.1~4 was 0.11 μs, 0.12 μs, 0.16 μs and 0.15 μs， respectively.