Abstract: Based on the analysis of thin impermeable layer in Hancheng Mining Area, the risk of Ordovician limestone water inrush in Sangshuping Coal Mine was studied. The reconstructed thickness of the top layer of Ordovician limestone was calculated. Using directional drilling technology and grouting technology, the top layer of Ordovician limestone of 3110 working face in Sangshuping Coal Mine was treated. Geological structure and water abundance of Ordovician limestone of seam floor in underground coal mine were proved up. Meanwhile, water inflow of working face after mining was predicted. The method of Ordovician limestone water prevention and control mining above thin impermeable layer was formed. The lower limit of safe mining in coal mine area was extended.