Abstract: Aimed at the engineering problems of goaf water disaster easy to happen in the goaf of the unknown goaf in the mine, taking No.11 coal seam of Taiyuan Formation of Shengli Coal Mine which belonged to reorganization and integration mine as an example, the mechanical model analysis, empirical formula calculation an d numerical simulation method were adopted, height of water flowing fractured zone and depth of failure zone of floor were analyzed and studied after the No.10 coal se am was mined and the overlying No.6 and No.2 coal seams were mined.Results showed that the maximum height of water flowing fractured zone was respectively 54.9 4, 30.49 and 33.67 m when No.10, No.2 and No.6 coal seams were mined, and the maximum floor failure zone depth was respectively 12.24, 2.55 and 1.25 m, based 0 n the relative spatial location of them, it was concluded that the water in the goaf of No.2 coal seam would not affect the mining of No.10 coal seam, and the water in th e goaf of the No.6 coal seam would come into No. 10 coal seam, and could bring great influences on the safety production of No. 10 coal seam. The scope of accumulate d water in unknown mined out area was accurately determined combine with several methods, including survey data, surface geophysical prospecting and underground geophysical prospecting, all this could provide references for risk analysis and range detection of water inrush in overlying unknown mined out area.