Progressive-collapse events of arch bridges have repeatedly happened in recent years, resulting in significant casualties and property losses. Based on a recent and serious progressive-collapse event of a stone arch bridge, this paper simulates the entire process of progressive collapse using the general purpose finite element (FE) program MSC.Marc. The simulation adopts a 3D FE model and performs nonlinear analysis using the contact algorithm in conjunction with the element deactivation technique. The potential causes of the progressive-collapse of the stone arch bridge are also evaluated. Furthermore, the importance of different components of the stone arch bridge is indexed with the conception of generalized structural stiffness, by which the most critical and vulnerable regions of the bridge can be identified. The research outcome reveals that the simulated progressive-collapse process agrees well with the actual process and the predicted critical regions are both correct and realistic. This study has also provided important references for analysis and prevention of progressive-collapses of stone arch bridges.