Abstract: In order to study the stability and water isolation property of the boundary　coal pillars after the mine is closed, FLAC3D numerical simulation software is used to the regularity of groundwater migration and water level rise as well as the variation of fault conductivity after the closure of the pit in Sanhejian Mine. The damage field and seepage field are numerically simulated, the seepage law under high water pressure is analyzed after the goaf is filled with water, the coupling between the surrounding rock damage field and the seepage field is evaluated. The results show that there is no overlapping conduction for the damage area of working face mining between Sanhejian Mine and Yaoqiao Mine, which meets the requirements for the safety of coal pillars. The development of seepage channels in mining rock masses is obviously affected by the mining of coal seams. Compared with non-conductive faults, the seepage field of water-conducting faults has a significantly larger scope. When the F19 fault is non-conductive and water-conducting, none of the plastic failure fields in the working face of Yaoqiao Coal Mine has penetrated the seepage field in the working face of Sanhejian Coal Mine, and the water isolation property of boundary coal pillars is good.