Abstract: Under the condition of high-intensity mining, the mine in Chenghe mining area enters the deep mining area with thin aquiclude, high pressure coefficient and complex structure. The arrangement of working face in the deep mining area following the previous goaf is bound to increase the depth of floor failure. Once the failure fracture is connected to the K₂ limestone aquifer and the Ordovician limestone water, it will directly form a recharge channel, which will affect the safe mining of the working face.Firstly, based on the geological structure characteristics of rock strata, the plastic failure mechanical model of four layer structure floors is constructed, and the theoretical analysis under four working conditions is carried out. Then, the displacement field, stress field distribution law and plastic zone development characteristics of floor rock mass under the influence of repeated mining are simulated and analyzed. Finally, the field test of floor failure depth was carried out in 23502 working face and 23503 goaf of Dongjiahe Coal Mine by using borehole strain monitoring and water pressure test method.The results show that: Using the plastic slip line field theory of the four layer structure floors, according to the depth of the active limit zone, the 23502 working face belongs to the third working condition, and the maximum failure depth is 18.32 m. The 23503 working face belongs to the second working condition, and the maximum failure depth is 15.83 m. Numerical simulation shows that the failure depth of the floor increases significantly under the influence of double-sided mining, especially under the adjacent coal pillar area, the maximum failure depth can reach 18.5 m, which is higher than the failure depth of 15.8 m in the single working face. Under the influence of multiple mining stress fields, the internal elastic core area is reduced from 23 m of single-sided mining to about 14 m. The peak abutment pressure under both sides of the coal pillar is always at a high level, and the maximum peak coefficient is 1.35 times higher than that of single-sided mining. The measured data of pressurized water show that the maximum failure depth of the floor of the 23503 goaf is 15.85 m; the drilling strain monitoring data show that the maximum failure depth of the floor of the 23502 working face is 18.3 m. The results of theoretical calculation are consistent with those of numerical simulation and field measurement. The research results can provide some guidance for the mining of coal seams on confined water bodies in Chenghe mining area and other similar mining areas.