Abstract: By analyzing hydrochemical data of groundwater in the unconsolidated sediments collected in 2004,it is found that hydrochemical features of groundwater are well accordant with the hydrodynamic zones in the Datong Basin.From the mountain area to the basin groundwater flows through the recharge,subsurface runoff area and discharge area,and groundwater is dominated by HCO-3 type,HCO3·SO-4 type,and HCO3·SO4·Cl-type water,respectively.Compared to groundwater in the medium-deep-seated aquifers,the major constituents groundwater in the shallow aquifers,which is characterized by more complex hydrochemical types to a greater degree because of intensive evapotranspiration owing to high groundwater level and arid climate from the mountain area to the basin area,and contamination induced by human activities.The quality of shallow groundwater tends to be better except the central part of the Datong Basin;while the quality of groundwater in the medium-deep-seated aquifers generally does not changes significantly.