Abstract: By studing on the hydrochemistry of karst groundwater before and after mining activities in Fengfeng coal mining area,The paper found out that the characteristics of hydrochemistry had been significantly changed. Firstly,the contents of Na⁺+K⁺ 、Mg²⁺、SO^2- ₄and the mineralization in the karst groundwater were more higher than the pre-mining periods. Secondly, besides the hydrochemistry type, the recharge source and hydrodynamic features had become more complicated and diversified. Thirdly, water quality becoming deterioration and human contamination had been getting stronger. Fourthly, the original flow system had been disturbed, which was turning the complex flow system into a simple one. Finally, the strong runoff zone had been vanished, while the middling and week runoff zone well developed. Groundwater velocity had become significantly slowly, hydraulic gradient become higher; the mineral capacity dissolved more dolomites; heavy metals detection rate and concentration more increased and hydraulic connection closed. Karst groundwater had been receiving reverse recharge from bedrock, pore and river water.