It is a key step of finite element method analysis to generate engineering structure mesh. The continuous conceptual model of discontinuous substance is studied. How to select similar-continuous micro-particle size is researched. The continuous conceptual model of soil body and the continuous conceptual method of geotechnical engineering are approached based on the deep mixing pile composite foundation. The results show that finite element method mesh generation based on material-continuous-nature need to more consider, and the minimum of the element size is those of similar-continuous micro-particle and the maximum is limited by the scope of geotechnical engineering project. While the material continuous nature is considered, the continuum theory would be satisfied to simulate engineering structure with finite element method.