For the composite random reliability problem, based on the Markov hypothesis of the dynamic response spanning action, two procedures of conditional probability explanation are accomplished: to derive the 2nd-order approximate expression for the calculation of the dynamic reliability of the random structure based on Taylor expansion method; secondly is to determine a mathematical sampling technique based on the Kriging model derive from the statistical analysis. Between them, the sampling procedure by the Kriging interpolation model meets the nonlinear correlation among dynamic reliability and structural random boundaries. Consequently, the finite element results can be used instantly to anatomize the significance of random structural parameters on dynamic reliability, avoiding the tedious and cumbersome theoretical derivation. The numerical example outcomes demonstrate that the numerical sampling method established upon the Kriging model is inconsiderate to the ratio to represent the dispersion and has additional benefits in computational verisimilitude and calculation productivity