The 2304 tailentry was close to YF20 fault. In order to find out rich water of sandstone on the rock box of YF20 fault as soon as possible and eliminate roof water inrush induced by mining in the working face, sandstone water of rock box on YF20 fault was probed forward. The practice showed that advanced dewatering of sandstone roof in 2304 face could reduce roof water yield and water imtensity during mining period, which provided reliable hydrogeological data to mining in working face, ensure safe mining and it was an effective and practical roof water treatment technology.