Abstract: Due to the random distribution of geotechnical data and the sliding surface, it is more significant to evaluate slope stability and to design a slope by random searching technique and failure probability method. In the paper, the lowest position of the most dangerous sliding surface and its dIp angle, as well as the load combination reflecting the maximum failure probability of the entrance high slope of Xiaolangdi Reservoir, Yellow River, China, are given by random searching technique and probability method. At the end of the paper, the author points out that design of a step slope with 1:0.2 gradient has an advantage over that of the vertical one. The results could also be provided as a scientific basis for determination of depth and width of slope reinforcement .