Abstract: Environmental isotope study confirms that the strong runoff zone of karst groundwater in the Shangwang-Xitou-Heichi area in the middle part of the karst groundwater system in eastern Weibei, Shaanxi, is a main runoff area of karst groundwater in eastern Weibei. Karst water in the strong runoff zone takes an active part in the modern water cycle, with an average residence time of 51 years, and so has a relatively strong renewable capacity. 14C evidence shows that the karst groundwater south, north and southeast of the strong runoff zone has a history of more than 10000 years belongs to an unrenewable resource. The isotope EPM model calculation indicates that the hidden karst water system in the strong runoff zone has a natural recharge rate of 87.55 mm/a, a storage capacity of 9.62 billion m3/a and a mean storage coefficient of 0.029. The above-mentioned results are in the main in agreement with the results of hydrogeological exploration. The environmental isotope study offers direct evidence for the cycle intensity and renew ability of karst groundw ater, supplem ents and enriches in-form ation of karst groundw ater m ovem ent and provides key data for the quantitative evaluation of renew ability of hidden karstgroundw ater resources in the study area.