Abstract: In this paper the instability-failure process of floor due to confined water inrush is numerically simulated by using the Coupling System of Flow & Solid in Rock Failure Process Analysis(F-FRPA^2D) that has be en recently developed by CRISR,Northeastern University.In this numerical model the fluid pressure transmission during the rupture-failure process of material is achieved by the coupling and iteration of flow-damage of an element.According to the results of the simulation the instability-failure mechanism of floor associated with the confined aquifer is analyzed and the position where water inrush is liable to happen is predicted.The results are in the main consistent with t he phenomena at the site,which indicates that the F-RFPA^2D,as a newly developed numerical simulation code,can be used to study water inrush from the confin ed aquifer through the floor.