Abstract: In existing research regarding the Member Discrete Element Method (MDEM), an assume must be satisfied that the tangential spring of contact constitutive model is only used to reflect pure shearing deformation caused by shear force. However, the deformation obtained by the above assume is inconsistent with that caused by shear force according to the bending beam theory. To address this issue, the tangential spring of the contact constitutive model was redefined, and the calculation formula of the tangential contact stiffness coefficient with or without considering shear deformation was systematically derived based on the principle of energy equivalence. On this basis, the refined plastic hinge method of the MDEM was proposed to describe structural plastic development, and the elastic-plastic contact constitutive model between particles was deduced. The static and dynamic elastoplastic behavior analyses of two large-scale reticulated shell structures were carried out by MDEM programming, and the correctness of the contact constitutive model and the applicability of the refined plastic hinge method were verified. It systematizes the basic calculation theory and supplements the elastoplastic theory of the MDEM. A new idea is provided for the static and dynamic analysis of structures.