Taking the Shijiazhuang, Hengshui and Cangzhou areas as an example, the authors introduce their knowledge about the formation law of deep-lying groundwater gained through the application of isotopic techniques, together with a synthetic analysis of hydrogeological structure of the groundwater system and the hydrodynamic calculation of the groundwater age. The deep-lying groundwater in the piedmont area is mainly recharged by infiltration of precipitation at top of the alluvial-diluvial fans, and its age is 0 to 30 thousand years. Groundwater in the east-central area and coastal area is mainly recharged laterally by groundwater flow originating from the Xing-tai area located southwest of the study region. Because of the long flow path, small hydraulic gradient and low permeability, the water age can be as high as 30-300 thousand years in these areas. Thus the authors come to the conclusion that the recharge and storage capacities of deep-lying groundwater in the region are very low. This provides important grounds for rational exploitation of deep-lying groundwater resources in the study region in the future.