Theory and engineering practice show that the hydrogeochemical method is the one of effective approaches to groundwater hazard prevention and control in coal mines. Taking Pingdingshan and Feicheng coal mines as examples, this paper discusses some applications of hydrogeochemical methods to the study of groundwater hazards. In the Pingdingshan coal mine area, environmental isotopes and cluster analysis techniques were used to confirm and clarify that the conceptual model of groundwater systems (i. e. classification of local and transition flow systems) previously obtained is only suitable for the Cambrian limestone aquifer. The sandstone aquifer receives rainfall recharge in the middle-northern hilly area and groundwater in the sandstone aquifer probably recharges the thin-layer limestone aquifer. In the Feicheng coal mine area, it is proven by the groundwater trace tests that faults GF9, F7-1 and F7-3 have relatively high permeability within the test sections, and groundwater in the Ordovician limestone aquifer could flow through those sections and into gushing water points beneath the coal mines in different passages and at different velocities. These faults, therefore, are considered main threatening to the mining safety.