Abstract: The Chaobaihe alluvialdiluvial fan is located in the northeast of Beijing as an important water supply region for Beijing urban area. Over the last 30 years，especially since 1998，groundwater system has changed significantly under the dual impacts of climate change and human activities in the form of precipitation decrease and groundwater exploitation. Results from series analysis of changes in precipitation，surface runoff，groundwater regime and groundwater storage show that the region has undergone a marked change in groundwater. Among the reasons for water table decline and storage reduction，decrease of precipitation accounts for approximately 24％ while human activities，such as industrial and agricultural use of ground water，use of wells designated for emergency water supply and reduced infiltration of surface water are responsible for the other 76％. Series analysis of precipitation from 1724 to 2007 shows that average precipitation amount from 2000 to 2007 is only three quarters of the total average value，which is the reason for the decreasing of surface water and direct recharge. Analysis of the relationship between precipitation and groundwater recharge shows that when precipitation decreases by 10％，groundwater recharges decreases 10％ accordingly. The impact of human activities on groundwater is remarkable based on groundwater monitoring. Changes in groundwater storage has been calculated based on the monitoring data of groundwater table and specific yield. According to the mass balance equation，deficit of precipitation led to a decrease of 0.75×10.8m3/a in the groundwater recharge，accounting for 24％ to the total storage which is 3.1×10m3/a，while the human activities，like increased groundwater extraction，reduces the groundwater recharge of 0.09×108m3/a which contributes about 3％ to the total decreased groundwater storage，and the exploitation of emergency water sources decreases the groundwater recharge of 1.60×108m3/a which contributes about 52％ and cutoff of recharge from surface water reservoir decreases 0.66108m3/a which contributes about 21％. In one word，the human activities contribute 76％ in total to the decreased groundwater storage，as main driving factors controlling groundwater system in the study area. The study gives a potential method based on water mass balance to differentiate the impact of climate change from human activities on groundwater system to promote the sustainable groundwater management and utilization. The southtonorth water transfer project is underway to alleviate the water shortage in the North China Plain and it is expected that the diverted water will come to Beijing in 2014.Before that date，it is necessary to continue mining of groundwater. It is with hope that groundwater table can be restored after the water diversion is implemented. However，due to high uncertainty of climate change，there is still a possibility that consecutive dry years may occur after the water transfer project. As a result，there is a high risk for the plan of water conservation in wet years. Therefore，it is recommended that the use of emergency wells should be reduced or even stopped in order to restore the groundwater in Chaobai alluvialldiluvial fan so it will be possible to extract water under emergency situations.