Abstract: The deterministic methods widely used to evaluate seepage stability of earth dams were perfect.But the safety of earth dams could not be indicated reliably by the results of safety analysis due to the incomplete consideration of variation of parameters of dam material.In the seepage stability analysis of earth dams using probabilistic and statistic methods the uncertain factors of dam materials could be taken into account.First,the probability distribution of physical parameters of dam materials was obtained by use of the statistic methods.Then the principle of reliability analysis was used to construct the function of seepage failure of earth dams,and the effect of effective unit weight and angle of internal friction of soil,seepage coefficient of dam body and foundation were also analyzed.The geometric methods were adopted to calculate the reliability index of seepage failure of earth dams,furthermore the seepage failure probability of earth dams was also obtained.Taking one earth dam for example,the method mentioned above was used to analyze the seepage stability of earth dams.It was shown that the great variation of effective unit weight and angle of internal friction of soil could result in the increase of seepage failure probability of earth dams,the effect of variation of angle of internal friction of soil was greater,and the seepage failure probability of earth dams was sensitive to variability of dam seepage.In addition,the increase of water level in reservoir would also induce great increase of seepage failure probability of earth dams.