On the basis of analyzing hydrogeological conditions, the spatio-temporal variation of hydrochemical characteristics of groundwater in Kuji water source area of Ordos basin is systematically researched. The chemical composition, spatial distribution, and variation of hydrochemical type were affected by geographic, geomorphic and runoff conditions. Results showed that hydrochemical type changed as a whole along the direction of groundwater flow from  the peripheral watershed towards the interior and from the internal watershed towards the peripheral. The main negative ion gradually changed from HCO₃ to HCO₃•Cl and further HCO₃•SO₄•Cl, and then SO₄•Cl. In vertical direction, close hydraulic connection between the middle layer and shallow layer groundwater was found, and their partition was not obvious. Due to close hydraulic connection in vertical direction for Cretaceous aquifer of huge thickness and the depth of groundwater, the groundwater quality is less affected by seasonal change.