Abstract:The Ordovician karst water is one of the hazards in the safe mining in North China. Mining above aquifer is one of the effective methods,which is used to exploit the coal seam threatened by water-inrush from floor. In order to analyze the water inrush risk from coal seam floor above aquifer,a water pressure loading system of the confined aquifer on coal seam floor is self-developed to realize the physical simulation of the confined aquifer acting on the aquifuge in floor using pressure water bags. The deformation and failure characteristics of aquifuge in floor are analyzed to obtain the rules of the fractures of floor developing,extending and running through each other. And then,the water-inrush passageway will be formed. The research results can provide references to the mechanical mechanism of water-inrush from floor.