Based on water quality monitoring data of Daning surge tank from 2009 to 2017，the variation characteristics of water quality were analyzed by Single-factor evaluation method and the comprehensive pollution method.Results are as following，water quality from upstream is the main factor that determines the water quality of Daning surge tank；water quality potential risk factors in Daning surge tank are mainly nitrogen and phosphorus；low-flow and low-velocity Water delivery by pipes in hot summer days should be avoided；using biological manipulation to address regional water security threats if possible to improve the water quality of Daning surge tank，promote the security rate of urban water supply in Beijing.