Numerical manifold method (NMM) is a numerical system which contains manifold method

finite elements and discontinuous deformation analysis (DDA). NMM can return to finite elements when physical elements and mathematical elements in NMM are superposition completely; and contact theory is removed. It will be verified by plate compression numerical experiment in the paper. In previous NNM

the problem of mass-conservation is neglected

which the weight of the physical elements will change with changes in its volume; so there are certain error in the calculation results. Mass-conservation can be realized by changing the elements density in the process of calculation; that will perfect the theoretical basis of numerical manifold methods.