Abstract: Mining upper limit can be increased, weak containing water layer can be disturbed by some of fracture belt, and defending stone column of coal and rock can be retained. Since the LongDongmine’s underlay rock with the properties of separating water and resisting fracture, by analyzing the fourth groundlay’s features of containing water, separating water and wind oxidation belt, researching the rock type, structure and mechanical properties. In this paper, the method of borehole water flushing and the both ends blocking technology of underground upper inclined borehole have been used to determine the mining upper limit. The LongDongmine’s mining upper limit be advanced completely by the way of trying mining.