The three-dimensional Numerical Manifold Method(NMM)is studied on the basis of two-dimensional numerical manifold method.The three-dimensional cover displacement function is studied.The mechanical analysis and Hammer integral method of three-dimensional numerical manifold method are put forward,the stiffness matrix of three-dimensional manifold element are derived and the dissection rules are given.The theoretical system and numerical realizing method of three-dimensional numerical manifold method are systematically studied.As an example,the cantilever with load on the end is calculated,the results show that the precision and efficiency is agreeable.