Abstract: According to Tongxin Coal Mine mining technological conditions and surrounding rock mechanics parameters, the motion characteristics of the overburden at fully mechanized caving face were analyzed by discrete element numerical simulation software UDEC. The height of caving zone was determined based on the overburden's displacement change law. Comparing the simulation results with the theoretical calculation of fully mechanized slicing method and fully mechanized caving mining and measured data, the results indicates that the simulation results match with fully mechanized caving mining theoretical calculation and measured data. While the deviation compared with fully mechanized slicing method is fairly large, which explains that the original theoretical calculation formula is no longer applicable to fully mechanized caving mining, and using numerical simulation method to determine the height of caving zone is one of feasible methods.