Abstract: In this article, method of critical sliding field theory is applied to search the dangerous sliding surface of slope under the condition of the slope angle and get the critical state of slope under the conditions of different safety factors, which can determine the optimum slope angle of the slope design, then four kinds of limit equilibrium analysis methods are applied for the safety evaluation so as to get the optimized design scheme of open-pit mine slope. 3D numerical simulation technology is used at the same time to analyze the open-pit mine on the boundary of the stress field distribution characteristics, and it is concluded that the stress distribution of the area and value is small, and it won't produce destructive deformation, which proves the rationality of the design of slope.