Abstract:The key of mining the coal seam threatened by confined water in Ordovician limestone is the understanding of the failure mechanism of floor rockmass and determination of affecting depth by mining. The affecting depth is usually acquired according to the change of permeability in floor rockmass. The permeability of the floor rockmass is closely related to the stress field of floor rockmass. Based on in-situ measured data,mechanical parameters of rock and method of displacement back analysis,the floor stress field of coal face No. 1237 in Zhaogezhuang Mine is firstly given,then the permeability coefficients of floor rockmass is computed,and lastly the relationship between stress field and permeability coefficients is determined.