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To enrich the research methods for studying the development law of bed separation, this paper takes the upper 08 working face of 221 in Shilawusu Mine as the research object, and comprehensively determines the location of bed separation through distributed optical fiber (BOTDR) and fixed-point optical fiber. The particle flow code (PFC2D) is used to study the pattern of the separation layer development under the conditions of large mining height and large mining depth. The results show that, as the working face advances away from the cutting hole, the separated layer develops intermittently from the bottom to the bottom of the key layer, and the depth of separation layer development is around 440 m, 396 m, 376 m, 331 m, 321 m and 296 m, and the layer stops at the bottom of the main key layer of coarse sandstone. The overburden transport mainly goes through the stages of subsidence of the lower key layer, rapid subsidence of the upper sub-key layer, development of overburden movement towards the bottom of the main key layer of coarse sandstone, and transport of the main key layer. The separated layer position is proportional to the advancement distance of the working face, and the development of the separated layer is mainly divided into three stages, which are gestation (Ⅰ)-accelerated expansion (Ⅱ)- compression stage (Ⅲ).