Abstract: According to the factors which affect the width of waterproof coal pillar for stope fault,this paper pointed out that the width of waterproof coal pillar for stope fault should include the coal pillar width of mine pressure and fault affected zone.By using elastic plastic limited equilibrium theory,hydromechanics theory and soil mechanics theory,this paper derived rigorously the formulas of each affected zone width from the mechanical points,and proposed the calculation method of waterproof coal pillar for the width of stope fault,which could provide theoretical guidance for mine waterproofing work in the future.