Based on the karst groundwater system characters of the fault zone water source site in Yishan along Xilong River, the authors established the numerical model for real flowfield of karst groundwater of the water source site, in order to simulate and forecast the groundwater level dynamic variation, and then carried out the assessment of the permissive karst water exploitation yield. It was concluded that a yield of 28 000 m3/d was feasible for the permissive karst water exploitation yield.