Abstract: In order to provide theoretical basis of roof water disaster prevention of No.3 coal seam in a working face after fully-mechanized top-coal caving, empirical formulas in Regulations of building, water, railway and leaving coal pillar and mining pressed coal in main shaft and drift, numerical simulation and underground up-hole water injection method by intervals were respectively adopted to study height of water flowing fractured zone of overburden strata of working face. Estimated values by empirical formulas are 51.1 m and 59.0 m respectively, calculated value by numerical simulation is 63.5 m, and measured value is 65.4 m. Height of water flowing fractured zone under the researched geological condition is about 63.5-65.4 m after comprehensive comparison and analysis. Sandstone aquifer of Shanxi formation is in the water flowing fractured zone and belongs to direct water filling aquifer. The water flowing fractured zone is not spread to Shihezi sandstone aquifer and Neogene loose aquifer. Normal fully-mechanized top-coal caving will not influence on water gushing in working face directly.