Abstract: The overlying rock mass deformation induced by mining is complex mechanical issue in metal mine because of its complicated conditions. Mining operations could change original stresses distribution of surrounding rock, that lead to stresses redistribution of overlying rock then reach a new balance. Structural planes have some influence on overlying rock deformation and failure when they developed and connected. for this situation, we built a 2-dimension discrete element method model utilized in Udec, and analyzed break characteristics and mechanisms of 2-rock-bridge and 4-rock-bridge. We also conducted some comparative studies of stress relief regulation in roof rock. We chose three experimental groups, which joint conditions are 0°/90°, 45°/45°, 20°/70°respectively, to analyze deformation mechanism of rock mass movement. by numerical simulation experiment, we demonstrated the ground movement characteristic and subsidence region. the experimental results have consistency with monitoring data of surface subsidence by GPS.