The　NMM　(numerical　manifold　method)　has　shown　its　ability　to　solve　continuum　and　discontinuum　engineering　problems　in　the　same　framework.　In　the　present　paper,　the　vector　sum　NMM　(VSNMM)　is　proposed　to　investigate　the　stability　of　slopes.　With　the　(vector　sum　numerical　manifold　method)　VSNMM,　the　FOSs　(factors　of　safety)　of　slopes　are　obtained　using　the　real　stress　fields　of　the　slopes.　Compared　with　the　limit　equilibrium　methods,　the　deformation　and　stress　field　of　a　slope　can　be　obtained　using　the　VSNMM.　Besides,　the　computational　cost　of　the　VSNMM　is　much　less　than　that　of　the　strength　reduction　numerical　manifold　method　(SRNMM),　since　only　one　elasto-plastic　analysis　is　needed　in　the　VSNMM,　while　a　series　of　elasto-plastic　analyses　is　needed　in　the　SRNMM.　Based　on　the　VSNMM,　the　stability　analyses　of　two　slopes　including　a　homogeneous　slope　and　an　inhomogeneous　slope　with　three　different　materials　are　conducted.　The　numerical　results　based　on　the　two　slopes　show　that　the　VSNMM　can　accurately　calculate　the　FOSs　of　the　slopes.