Abstract: Based on the special mining conditions of 9 coal under Double threat of the extremely thick igneous rock and ordovician limestone water，the water inrush mechanism of coal seam floor is analyzed under extremely thick igneous rock according to hydrogeological condition theoretically；study on the different roof control and ordovician limestone water press to the influence of coal floor stress distribution and deformation by numerical simulation.The results show that filling mining and forced caving than hydrophobic step-down to reduce disturbance and destruction of coal floor effect is remarkable under the condition of extremely thick igneous rock roof，and then put forward to filling or forced caving mining technology is given priority to with hydrophobic step-down technology of water proofing. By 2911 working face mining practice shows that this scheme could effectively reduce the water inrush risk.