Abstract: In order to analysis the fault activation mechanism of coal mining Stope floor, in this paper, considering mine-induced stress and groundwater pressure it have, we use theoretical analysis, numerical simulation, laboratory testing and other methods to do analysis in Sima coal mine field. The expression formulas of failure depth of complete floor and the floor of the fault during coal mining is deduced. The influence of the stress change on the permeability of fault during the process of coal mining is studied by using the permeability test of fault zone filling and the FLAC numerical simulation software. And through the field test, fault connectivity test, it prove that the barrier water capacity of the fault zone of the Sima mine is weak.