Deformation of slope for all section is almost the same while the width of slope along the strike is large enough, that is plane deformation. If the width is small, then cannot analyze according to the plane problem. According to above method, slope deformation of concave base is 3D problem if excavates a limited width concave conveyor belt alone the slope dip in open-pit mine. In this article, the relation between excavation width and deformation is analyzed by 3D numerical simulation method, on the basis of some mine actual geological occurrence conditions, meanwhile, calculative equation among deformation geometry and limit equilibrium is established to evaluate concave base slope stability. Concave base slope for conveyor belt is 32% for deformation of plane mode slope in light of numerous simulation result, and the stability coefficient can be improved by 0.5 through case studies analysis. So, the safety of belt transport system is ensured.