Abstract: Emergency groundwater source field locates in Sijiqing region, which is a covered karst water source field; the water intaking horizon is the Ordovician aquifer. Ordovician karst water is back-up water resource of Beijing city for safe water supply with good water yield property and excellent water quality. Based on comprehensive analysis on the Ordovician karst groundwater hydrogeologic characteristics and pumping test data, groundwater table is predicted with correlation analysis method in this paper. Exploitation potential of karst groundwater is analyzed in view of water-bearing capacity and groundwater flow field as well as groundwater resources to ensure the groundwater can be used as back-up water source for city water supply in the event of water crisis. The results indicate that, karst groundwater system is characterized by developed karst fissure, good recharge condition and good water quality, great groundwater flow intensity. The emergency karst groundwater source field has a 60 000 m3/d of the exploitation potentiality. When water source field increase emergency extraction of 60 000 m3/d, the predicted groundwater depth is 52.94m, which can met the demand of existing water facilities and does not affect the other wells’ normal running.