Fujian Province is one of Coal shortage for the southern provinces, under the premise to ensure safety of existing and the nowadays conditions of mining as much as possible recovery of coal resources under the old empty water. Uncle YongDing County, Fujian Province Coal mining under the old empty water, for example, to carry out joint working face with a high degree of water flowing fractured measured. Because the field complex geological conditions, the use of empirical formula and numerical simulation method to calculate the upper mining limit, and greater access to the actual situation. Only through in-situ measurement, to obtain specific geological mining conditions of the mine under the true information in order to obtain the actual situation of the mine found the correct data. To this end, this small coal mines in Fujian Province in the first the new technology that upward hole with a multi-stage water underground observation method was used to observe a high degree of fracture of Water, through in-situ construction and arrangement of holes and cracks under the conduction of water with a high degree of observational data analysis and results showed that after two coal face showed continuity with the overlying rock fracture characteristics, top boundary height 43.4m, 3.5m thickness calculated in accordance with mining, mining split ratio of 12.40.