As an important water source of Beijing, Pinggu basin provides an important support for the Beijing municipal water supply, in order to better understand the lateral recharge of Pinggu mountain area and the recharge and drainage relationship between Quaternary groundwater and underlying bedrock karst water in Zhongqiao water source area, establish and improve regional groundwater flow model, calculation and evaluation of regional groundwater resources, and put forward groundwater reasonable utilization and protection measures.Methods: Based on the basic theories of water cycle and hydrogeology, the regional hydrogeological conditions are analyzed. and the recharge sources, recharge relations, recharge elevations and recharge ratios of different recharge sources of regional groundwater are analyzed by hydrochemistry and isotope hydrology Results: The quaternary water and bedrock karst groundwater in the study area all come from atmospheric precipitation, and the chemical type of groundwater is HCO 3-Ca.Mg. The quaternary loose pore water and the underlying karst groundwater are supplied by The bedrock karst water in front of the North Mountain. According to the estimation of 2H, 18O and T values, the ratio of lateral recharge of karst water to vertical precipitation infiltration recharge of Quaternary shallow groundwater in Zhongqiao water source area is 57: 43. The ratio of bedrock karst water to lateral recharge of mountain karst water and vertical overflow recharge of Quaternary pore water is 87: 13.Conclusions: Mountain karst groundwater not only supplies the underlying bedrock karst water in the plain area, but also supplies the quaternary loose pore water in the plain area. There is a close relationship between bedrock karst water and Quaternary loose pore water in the water source area of Zhongqiao.