Abstract：The residual thicknesses of aquifuge and mining reactivations of the fault are the key factors to control the water inrush when mining is near the large-scale fault with karst aquifer under the floor. Taking the mining working face of deep coal seam under large-scale thrush-fault with high water pressure of Ordovician karst at Liuxin mine in Xuzhou mining area as a case，the numerical simulation，the mechanical analysis and the geological evolution process have been performed based on the viewpoint that aquifuges exist in Ordovician top and can be considered as key aquifuges，which can guarantee the safe mining of the working face. The research results show that in the experimental area，there are carbonatite aquifuge about 118 m in thickness，in which the karst cave is refilled and undeveloped. The fault in natural state is not water-conducting one；and the part of thrush-fault between coal seam in drop side and the Ordovician roof(about 60 m) in upthrust side is reactivated by mining，but the part of thrush-fault in top Ordovician aquifuge is not reactivated. If the Ordovician top is saturated with karst water，the water driven by high water pressure may infiltrate to the working face along the reactivation part of fault，which means the water inrush will occur. The aquifuge existing in Ordovician top is the primary reason for the mining safely around the fault.
