Abstract: Based on the test principles of geological mechanics model and engineering geological and hydrogeological conditions of Nansi Lake, 12 geological mechanics model are established. By simulating the coal mining under the lake, the failure process of sandstone and limestone above the coal and the formation process of ground mining basin are studied. By measuring the change of perched water level and groundwater level with coal mining under the lake, the water level of the lake is studied. The seepage process from the lake to the mining pit is also studied. If there is a clay layer with depth of 2 to 3 m, the amount of leakage will be very small. The water in the lake will not be affected. The perched water level will cyclically decline with coal mining. But when the coal mining stops, the perched water level will gradually recover. For the restoration of the perched water level to its original 95%, it needs about 1 year under the engineering geological and hydrogeological conditions of Nansi Lake.