Abstract: In this paper,seepage models are put forward in the view of hydrogeology,which are based on the actual situation.By using the computer simulation method,authors get thicknesses of safe protection layers of two hydrogeology condition when mining under Huai-river,and study the leakage from the upper aquifer to the mining face.The result shows that the barrier is the coal deposits,not the Quartenary mudstone,when it is composed of crystal mudstone,and the thickness of the barrier is 15 meters.If the Quartenary layer is composed of mudstone,containing clay and gravels,only the layer of thickness of 6.5 meters can protect the water effectively.The leakage of the whole mining area is less than 0.4 m³/min.So the mining upper limit can be raised greatly.