Abstract: Eight natural limit-state loess high slopes are measured in Xixian-Lishi area of Shanxi province. Then the geologic models are built. Meanwhile,soil test data of 592 groups soil samples from investigation reports of the engineering geology are collected,counting the physical and mechanical parameters of loess in study area according to chronologic age. Soil test data of 9 sites along Linxian-Lishi road are selected. The parameters c, are statistically analyzed for the variability of loess simultaneously. The coefficient of variation for the value of strength parameters c, are combined,carrying out the simulation of reliability by Monte-Carlo method. The results show that the stability coefficients of these slopes are between 0.96 and 1.14. The probability of failure are between 33.0% and 61.8%.The natural analogy method is used to analyze two natural limit-state loess high slopes with the heights of 50.5m and 80.8m,respectively. The analysis shows that for the slope of 50.5m high if the design requires the probability of failure no more than 10%,the slope ratio should not be more than 1:1.81 under the average combination of variation coefficient(COVc=0.66,COV=0.28). For the slope of 81.8m height if the design requires the probability of failure no more than 10%,the slope ratio should not be more than 1:1.94 under the same combination of variation coefficient.