Abstract: Recently, the center of coal mining is transferring from the east to the midwest in China. But in these regions, with the arid and semi-arid climate and fragile ecological environment, the mining is going to have a significant impact on the quite limited water resources. From the development of the preceding years, this problem has led to a seriously restriction on the coal production. Taking Shennan mining area in Northern Shaanxi for an example, the paper discusses the scientific problem of water preserved mining.In the analysis, the paper introduces water system to the above scientific problem and this system integrates the whole water resources in the range of the mining area. For the water system,before mining, the input is rainfall and output is the discharge of the surface run-off. All of the factors in this system keep in balance with a certain detained capacity within the mining area containing surface water, and water in sandy layer and burned rock. In comparison, after mining, the inputs will contain invariable rainfall and bedrock fissure water and at the same time, the output will decrease because of the leakage of the surface water under the influence of the mining. The above analysis obtains a conclusion-mining is going to increase the capacity of the retained water resources in the mining area and this increasing capacity is good for water preserved mining.