Some paper have presented the abstract element class of FEM, which the specific element class such as the triangle Element,the quadrilateral Element can be derived from. The substructure is the specific element class as the class derived form the abstract element class. The Object-Oriented FEM needs changing rearly when the sub-structural function is added to it. The Choleshi's disintegration of the sub-structural stiff is done and using the resolved triangular matrix many times can greatly reduce the work of the cohering matrix. The definition of the substructure class and the comparison between the sub_structural method and the normal method.