Abstract: In order to explore the optimal design method of slope morphology of open-pit coal mine, the south slope of Heishan Open-pit Mine was taken as an engineering example. Based on the simplified Bishop method and the theory of slope morphology effect, the slope with different concave and convex degrees under the two-dimensional perspective was designed, and the stability evaluations are carried out to obtain the better slope morphology. Based on the strength reduction method, the numerical simulation method is used to simulate the deformation process of the better slope morphology under the action of three-dimensional retaining. By analyzing the deformation characteristics, the optimal slope morphology is obtained by further improving the concave and convex degree of the slope surface. The results show that the slope morphology with better concave and convex degree under the two-dimensional design conditions is obtained. Due to the limitation of local slope stability, only two groups of composite steps can be arranged from the bottom to the top below the level of + 2385 m in the southern slope. The overall stability coefficient of the slope is 1.344, and the local stability coefficient is 1.204. Under the condition of three-dimensional design, the local and overall stability of the slope is improved under the influence of the support from the internal dump and the horizontal mining working side, and there is further morphological optimization space.  On the basis of the better shape, the optimal slope shape can be obtained by adding a group of combined steps to local steepen the slope section below + 2430 m level. In the process of numerical simulation , the deformation speed presented is relatively slow after entering the variable speed stage before critical instabilityand the final strength reduction coefficient is 1.20. Under the premise that the surface boundary and bottom boundary are unchanged, the optimal  slope morphology can ensure the slope safety and save about 3.84 million cubic meters of rock stripping in the first mining area.