Abstract：The rational design of safety pillar against water-inrush through stope sill faults is very important to the safety of coal mines. The characteristics of faults and the underground pressure are considered in the design. The coal body around mining area can be divided into two parts：the elastic area and the non-elastic area，where the latter does not have water-resisting function. The formulas to calculate the range of non-elastic area are deduced according to supporting pressure distribution characteristics. Based on the floor stress distribution characteristics in the direction of face advance，the developing direction of peak stress for underground pressure in floor is simulated and the mechanical models of water-inrush from floor are constructed. The results show that the passageway of water-inrush from floor consists of fault and broken floor strata caused by underground pressure. The condition of water-inrush from floor is that the depth of broken floor strata，caused by underground pressure，is not less than that of the join of peak stress line of underground pressure in floor with the fault. The formulas to design safe pillar against water-inrush from faults are achieved according to above results and a case study shows that the formula is reasonable.
