Abstract: By studying the micro characteristics of rock, the spatial structure, permeability and distribution of aquifer can be mastered. To fully understand the watery quality of direct water-filled aquifers of coal seam roof, taking Balasu Well Field as an example, by means of theoretical analysis, thin section observation and mercury injection tests, the microscopic characteristics of rocks in the direct water-filled aquifer of No. 2 coal seam roof in the future main mining of the mine are analyzed and studied. The results showed that, the lithology of the aquifers in Yan’an formation mainly consists 2 lithologic types which are fine lithoclastic feldspar sandstone and medium lithoclastic feldspar sandstone; there are 3 main lithologic types of the aquifer in Zhiluo formation, one kind of coarse lithoclastic feldspar sandstone more than Yan’an formation. The larger the grain size and the smaller the density in the sandstone aquifers, the conditions of porosity and permeability of the aquifer in Zhiluo formation are better than those in the fourth section of Yan’an formation. The occurrence of these two aquifers is not uniform and may affect the safety of mine production.