Using special hydrogeology survey, groundwater level observation, water pressure test, pit infiltration test, imaging well log technique and Hertz wave CT in the mining subsidence area and its nearby, failure mode of karst water under inclined coal seam mining in hilly area is studied. Contrasted surface infiltration capacity of limestone in 1955 with in 2011, it verifies that aquicludes and aquifers above goaf and near ground are damaged, therefore karst water in different aquifers become a unified water-bearing body. In the mining subsidence area, karst water forms a cone of depression, and water-bearing body of underground karst water supplied by vertical seepage is the main type of surface water infiltration. Outside of mining subsidence area, the surface water and the karst water are supplied by each other, and overland flow is the main type of surface water.