In view of the decreasing coal resource, there is not enough coal production to maintain the mine to survive. Based on the analysis of a working face in a coal mine, the paper analyzed the hydrographic and geological conditions and excluded the possibility of ordovician water inrush by using the way of water bursting coefficient. It was determined the F3 fault below the reservoir threatened 2# coal safety mining. After calculation and analysis, if mining hierarchical filling and remaining 60 m coal block was adopted, it could minimize the threat of mining under the reservoir. It provided a theoretical basis to achieve 2# coal safety mining under the reservoir, which could effectively alleviate the tensions of less coal production.