Abstract: Discrete element method has been an effective approach for simulating damage process of structures. A rectangular discrete element model is extended by applying nodal element and considering the non-linearity of concrete material in this paper. The failure criterion, formula and determination of analytical parameters such as spring modulus of the extended model are presented. The computational efficiency of the extended model is improved by applying double listing technique in the program. The collapse process of reinforced concrete frame due to explosion is simulated. Results show that the extended discrete element method achieves good simulation of collapse process of reinforced concrete frame structures.