Abstract: After the digging of a slope, its original stress equilibrium was broken.The slope would lose stability if the slope was high and steep enough. It could be kept stable continuously if an outer force from the prestressing cable-anchor beam acted on the slope, because of the stress state improve-ment. So far, there has been no reasonable methods to determine the degree of the improvement to the stress condition in a slope, and to determine the reasonable height of a single step slope, a first step discussion was presented.