Abstract: In order to provide the basis and safety assurance for the mining under pressure at Chengzhuang Coal Mine, we made a study of recharge runoff discharge and relative strata impermeability in Ordovician limestone top. The main technical means include field geological investigation, engineering test and laboratory test. The results show that Chengzhuang Mine Field is located in the main runoff zones, the groundwater flow from the northeast to the southwest and drain to the Yanhe spring finally. In addition, the rock stratum at Ordovician top about 35 meters has low penetrability, which could be seen as relative water-resisting layer. At last, we made a safety evaluation about the mining under pressure at Chengzhuang Coal Mine according to the water inrush coefficient formula after improved.