Abstract: The chemical properties of groundwater reflect the characteristics of geochemical field in which groundwater is located. The roof water-filled aquifers of No. 4 coal seam in Gajiabu Coal Mine include Jurassic sandstone aquifer, Cretaceous Luohe Formation aquifer and so on. The ion proportion of the aquifer water is similar, but the mineralization varies greatly, and obviously increases with the increase of buried depth. The isotopic properties of roof aquifer water in Gaojiabu Coal Mine show that the aquifer of Luohe Formation is recharged by surface water and atmospheric precipitation. According to the above hydrochemical characteristics, the basic idea of water prevention and control work in Gajiabao was determined. According to the salinity analysis of the outlet point of the working face, the water source and proportion composition of the effluent can be calculated, and it is put forward that the water source and the proportion composition of the effluent can be calculated. Corresponding measures were proposed to prevent and control water. It is of great significance to study the chemical characteristics of water in coal seam roof for the prevention and control of water in Gajiabu coal mine.