Abstract: Based on the analysis of the hydrogeological data of the first mining area in Zhaoxian Coal Mine, by using the research methods of theoretical analysis, similar material test and numerical simulation, the separation layer of overburden strata and water in the mining process of extra-thick coal seam is predicted theoretically. The dynamic development characteristics of vertical and horizontal fractures are analyzed, and the development status of separation layer in the sequential mining of multiple working faces in extra-thick coal seam is discussed. The results show that there is a space for water to separate from the bed at 253.64 m away from the top of the No.3 coal seam; the vertical fracture height increases in two stages including linear growth and stepped growth in the process of the working face advance; the horizontal fracture alternately develops and closes from bottom to top, and the development height of the horizontal fracture is positively related to the advancing distance of the working face; the 0.02 m horizontal separation fissure appears under the Yijun formation caused by the mining of 1307 working face, and the opening of the separation fissure is further expanded or even increased sharply with the mining of 1305 and 1303 working faces in turn; the method of floor water inrush coefficient is introduced to evaluate the risk of separation water inrush in Zhaoxian Coal Mine.