Abstract: In this paper, authors established a critical state equation for liquefaction of soil based on the ratio of seismic shear stress and pressure stress methods (RSC) and liquefaction probability through Monte-Carlo simulation using shear strength results of 26 groups of cyclic tri-axial tests from hydroelectric power stations in Sichuan Province. The reliability of liquefaction of soil layer of one hydropower station was then evaluated using the method. The results showed that it is reasonable to classify soil as slit and sand groups for statistical analysis. The ratio of shear stress and consolidation stress (RSC) follows normal distribution. The most dangerous case is a small dam with seepage suffering grade under VII magnitude of earthquake. The liquefaction venture increases as the depth of the sand-layer increases. The most vulnerable location in soil profile is the up-side of sand-layer. Therefore, treatment measures were recommended to strengthen the foundation of the dam to prevent liquefaction.