Continuum-based discrete element method (CDEM) is an explicit numerical method used for simulation of progressive failure of geological body. To improve the efficiency of contact detection and simplify the calculation steps for contact forces, semi-spring and semi-edge are introduced in calculation. Semispring is derived from block vertex, and formed by indenting the block vertex into each face (24 semisprings for a hexahedral element). The formation process of semi-edge is the same as that of semi-spring (24 semi-edges for a hexahedral element). Based on the semi-springs and semi-edges, a new type of combined contact model is presented. According to this model, six contact types could be reduced to two, i.e. the semi-spring target face contact and semi-edge target edge contact. By the combined model, the contact force could be calculated directly (the information of contact type is not necessary), and the failure judgment could be executed in a straightforward way (each semi-spring and semi-edge own their characteristic areas). The algorithm has been successfully programmed in C++ program. Some simple numerical cases are presented to show the validity and accuracy of this model. Finally, the failure mode, sliding distance and critical friction angle of Jiweishan landslide are studied with the combined model.