Abstract: The relationship between structural-system reliability evaluation and multi-normal integrals is analyzed, and the deficiency of the original Product of a Conditional Marginal (PCM) method for multi-normal integrals is pointed out. An improved PCM method adopting new measures for the calculations of conditional normal fractile and coefficient matrices is presented. The improved method firstly takes a numerical integration approach for the solution of bivariate normal distribution problems, which improves precisions of the fractile. Then, it updates the corresponding coefficient matrices, based on the precise fractile. It thus efficiently overcomes the inaccuracy of the original PCM method especially being used for the reliability evaluation of a series system. It also presents the details on how to implement the improved PCM method together with the explicit iteration algorithm, which is very efficient for element reliability evaluations. The availability and practicability of this improved PCM method is illustrated through two examples finally.