Abstract: Progressive collapse is defined as the collapse of the whole building due to local weak stories or weak zones. Though collapse should theoretically be avoided for any building under any earthquake, it is necessary to study the collapse behavior of buildings to acquire a better understanding of the collapse mechanism and to find efficient methods to prevent it. The collapse process highly depends on the feature of the whole structural system, so numerical simulation becomes a major method to study it. With the numerical program developed by the authors for the collapse simulation of complicated structures, the highly nonlinear behavior of structural elements can be properly simulated. Two real buildings are analyzed to study the failure mechanism of the structure. The models proposed are reasonable to study the seismic collapse mechanism of high-rise buildings.