A mine in the transition from open-pit to underground mining is designed to use pillarless sublevel  caving mining method.In order to ensure the safe production of mine and reduce the impact on the geography and environment around the surface,an ore extraction model was established with Flac^3D mining software,and boundary conditions were introduced.The elastic-plastic changes in the mined-out area and the rock displacement were analyzed.The movement range of the rock was delineated,and the rock displacement angle was determined to be 65°.The simulation results can provide technical support for deep mining and safe production for mines.