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In order to research on the mining-induced permeability characteristics, based on the degree of difficulty of gas-drainage, by means of SF6 tracer gas and drainage statistical data, the permeability characteristics of protective layer was studied. Through the experimental analysis, the permeability and the state of stress are relevant. Through the mining process of the protective layer, the permeability of the depressed coal seam experienced a slight variation. The amplitude of variation decreases with the increase of the distance between coal seams and the change will lag behind the working-face of the protective layer. [ABSTRACT FROM AUTHOR]