Abstract: Mining damage of mine boundary coal pillar in closed mine could weaken its water isolation ability, which easily lead goaf water in the closed mine to adjacent producing mine through damaging the mine boundary coal pillar and affect mine safe production. Taking mine boundary coal pillar between closed Shenzhuang Mine and producing Yuanzhuang Mine in Huaibei mining area as research objects, mining damage width of mine boundary coal pillar between S2Ⅱ313 working face in Shenzhuang Mine and Ⅲ3142 working face in Yuanzhuang Mine was researched by FLAC3d numerical simulation and theoretical calculation method. The mining damage width is determined 13.1 m according to the research results, which shows that the mine boundary coal pillar has been destroyed, and coal seam in boundary of the two adjacent mines has no water blocking capacity. On this basis, safety of the mine boundary coal pillar was evaluated. The conclusion is that there are risks of coal pillar water seeping and collapsing, and some measures should be taken out such as setting water-blocking curtain, grouting reinforcement and so on.