Abstract: The key point of mining safety is backfill stability in the mine which used in the filling method. And the backfill also could control the ground pressure and constrain the surrounding rock mass deformation. The filling mining method is widely used in metal mining engineering and the backfill is the substitution of ore body. There are some stages of backfill after injected into the worked out section, as phase change-consolidation-load bearing-support counter force-make the interaction with surrounding rock mass. The backfill, overlying rock mass, unexcavated ore body and surrounding rock mass form an interacted system of mining operation to resist the external load. The system deformation and stability is the key issues. The large backfill is formed in No.2 zone of Jinchuan Mine by mining in decades. The mining operation has carried out in the deep, so the stability of large backfill is effect on the work safety. This article, based on the actual mining condition of No.2 zone of Jinchuan Mine in China, described the elaborated boundary shape and simulated the backfill mechanical behaviour. The backfill have occurred overall deformation because of compression. The shear stress is the major factor of backfill and surrounding rock local failure. Finally, the hazardous area is curtained by yield function and shear stress distribution.