Abstract: The deep charging effect of dielectrics is one of main factors leading to satellite failures. The conductivity is a key parameter which determines how the accumulated charge will be dissipated through the dielectric materials. The exact measurement of the dark conductivity and the radiation induced conductivity is essential to the hazard evaluation of the deep charging. On basis of the charge storage and decay method, the measurement and the numeirical caculation of the dark conductivity and the radiation induced conductivity are discussed in this paper. The irradiation tests of two materials are performed at temperatuer of 20 ℃, with irradiation intensity of 5 pA/cm2 by using 90Sr-90Y β source. The surface potential of materials varying with time is measured and the conductivity is calculated by curve fitting. This method was used in charging assessment of a satellite, and the calculated result is in good agreement with the test result.