Abstract: A numerical study was performed using the discrete element code 3DEC to study the evolution and ground movement of the overlying strata caused by the mining of a deep coal seam using full-mechanized caving method.The numerical model was constructed based on the geological and geotechnical conditions of the 8512,8513 working face in the No.8 mining area of Chenjiagou Coal Mine.The parameters of the key layer and its controlling effects were evaluated based on the monitoring data from the case.The confidence level of simulated data and measured data analyzed by variance and regression analysis method is 0.95,which ensures the scientificity and rationality of simulation parameters.The simulation results show that when the width-to-depth ratio of the longwall face is 0.24,the rock layers below the key layer 2 are all fractured and damaged,the key layer 2 plays a role in controlling the subsidence of the overlying rock,and the rock layers above the key layer 2 will also have a layered structure during the movement process,The amount of subsidence reaching the surface is less than the deflection of key layer 2;when the width-to-depth ratio of the longwall face is 0.48,the bottom of key layer 2 is broken and the structure is unstable,which will cause a sudden change in subsidence;when the width-to-depth ratio of the longwall face is 0.72,the key Layer 2 is completely broken,but due to the action of the thick mudstone overlying the key layer 2,the development of the water-conducting fracture zone is inhibited,and the development height is basically stable,the height is 196 m,the ratio of the fracturing height-to-mining height is 16.3;the width-to-depth ratio of the longwall face is 0.96.At the time,the separation layer between key layer 2 of the overburden and its underlying rock layer is closed.The hinged structure of key layer 2 expands laterally and is accompanied by overall sinking.The underlying rock layer of key layer 2 continues to be compacted to a certain extent after breaking After that,the sinking will not continue,but as the mining area expands,the sinking basin develops laterally,and the surface is fully mined.This result can provide a theoretical basis for the evaluation of the mine's "three-under mining",provide scientific guidance for later mining,and provide a theoretical reference for the law of surface movement and deformation under the conditions of large mining depth and fully mechanized caving mining.