Abstract: Conventional prediction of water discharge in sandstone -rich coal mine is inapplicable because of poor sandstone crevice connectivity.Predicting aquifer aqueous area and non aqueous area by brittle rock percentage composition is a new applicable method.The bigger the brittle rock percentage the stratum is, the easier for tensile crevice to develops.The more water space develops, the more aqueous sandstone aquifer is.In this paper, the brittle rock percentage composition is defined as ratio of total stratum thickness to brittle rock thickness.The sandstone crevice aquifer water-rich area is partitioned by percentage composition.The water discharge of un-mined working face can be computed according to the brittle rock percentage composition of the mined working face, which provides a new method for preventing and controlling water disaster and designing drainage system.