Abstract: Cambrian-Ordovician karst water in northeast Datong coalfield exists beneath the coal seam floor with confined pressure, which is an important local water source. In order to ensure the safe exploitation of the coalfield and protect groundwater resources, the characteristics of the karst water system in the northeastern Datong coalfield should be analyzed. This work attends to make such an analysis in terms of drilling, logging, hydrochemistry, water level monitoring data, mining data and field investigation. It is concluded that the characteristics of elevation variation of the Cambrian-Ordovician karst top surface are consistent with that of coal syncline and the thickness of karst aquifer,which is very heterogeneous. Most of the research area is of weak runoff, with hydrochemical type dominated by HCO3·Cl-Na. The source for the supply of karst groundwater is from the overflowing supply of the overlying aquifer in west and infiltration supply in east. The water level in the research area is decreasing yearly with a tendency of increase, because of increasing artificial drainage sites and large artificial withdraw volume. The peak level of karst water in the research area is one to two months behind the rainy season. These conclusions have guiding significance for the safe mining of the coalfield and the rational utilization of karst water in the research area.