In view of the capacity of tailings reservoir is insufficient and land acquisition is very difficult for building new tailings reservoir after the mining transition from open pit to underground in Chengjiagou Iron Mine,a technical scheme, which makes use of dumped open pit for discharging tailings,is presented.According to the actual conditions of the mine,the mode and zone of tailings discharge are presented.Based on the above results,the stability of underground stope in the process of tailings discharge into the dumped open pit is simulated by 3D-finite-element numerical simulation method,the stability mechanism of the underground stope after tailings discharge into the open-pit is analyzed,and some engineering control measures are suggested to prevent potential problems.