Abstract: Aiming at the safety mining problem under loose surface aquifer water body in Barapukuria Coal Mine of Bangladesh, injection water leakage in upward slant hole method was put forward to monitor height of water conducted zone in first stope which adopted fully mechanized coal mining technology. Monitoring results indicated that the maximum value of the height was 61.46 m in research area. Meanwhile, a numerical simulation about height of water conducted zone was got by software FLAC^3D; the values were 65 m and 88 m separately in the first and the second level. After compared with the results from experience formula, the paper finally determined that the real maximum value of height and crack and mining ratio was 65 m and 21.67, besides the paper got a new formula to calculate the height of fractured zone of mid-hard roof with analysis of data regression.