Abstract: Due to the Ordovician limestone water pressure reached to 7.510.4 MPa in first exploration zone of the low group seam in Dongtan Mine, a large scale h ydrological additional exploration was conducted for the safety mining of the low group seam.A systematic analysis and study was conducted on the geological and hydr ological conditions of the exploration zone. Based on the circumstances, a hydrological conception model of the exploration zone was established and thus the relevant mathematics model was obtained. The underground water quantity and water quality computer simulation software system FEFLOW with full functions was applied to si mulate the Ordovician limestone water drainage and dewatering quantity in Ordovician limestone hydrological I area, I area and耳area in the first exploration zone. The simulation results were individually as 1 900, 0, 720 m3/h and the time required to drop to safety water table would be 10, 0 and 20 days. The simulation results sho wed that the pressure of the Ordovician limestone water could be dropped and the a safety mining of the low group seam could be realized.