Abstract: To investigate the development laws of separation space from initiation, development to compaction, the 1101 working face of Zhundong No. 2 Mine was taken as the research object. Based on the composite beam theory, the potential horizons where separation may develop were predicted, and the development characteristics of overburden separation under large mining depth and fully mechanized top-coal caving conditions were studied using the discrete element numerical simulation software UDEC. The results show that the development horizon of separation is proportional to the advancing distance of the working face, and the separation develops from lower to higher horizons as the face advances. Simulation results reveal that distinct closed "cavity" separations appear beneath key stratum 1 and the primary key stratum. The low-level separation beneath key stratum 1 has a short development cycle; during the process from fracture initiation to development, the underlying strata break and collapse, preventing the formation of a closed "cavity" separation. In contrast, the separation beneath the primary key stratum exhibits a longer development cycle. As the working face advances, the composite structure formed by key stratum 1 and key stratum 2 settles, generating separation fractures beneath the primary key stratum. These fractures continue to develop during the subsidence of the lower strata until the primary key stratum begins to bend and subside, at which point the separation development rate slows down. When the subsidence velocity of the primary key stratum exceeds that of the strata below the separation, the separation space starts to be compressed and is ultimately compacted.