Dagu River basin is an important water supply source for Yantai City and Qingdao City. This paper is in order to study the water chemical characteristics and genetic mechanism of Dagu River basin. Methods:Water samples, including 35 groundwater and 5 surface water, were collected from the upstream research area of Dagu River basin. Hydrogeologicalinformation, Piper terraph map, descriptive statistics method, Gibbs diagram and ion ratio were used to analyze the hydro- chemical characteristics and explore their evolution mechanism of the study area. Results:The results shown that the groundwater in Dagu River basin is weakly alkaline. HCO-3, SO2-4 and Ca2+, Mg2+ were the dominant anions . All of most of samples belonged to HCO-3·SO2-4—Ca2+·Mg2+water type . The hydro- chemical characteristics of Dagu River Basin are affected by water—rock cation exchange, rock weathering and dissolution are the main controlling factors. Moreover, the cation exchange is active. Conclusions :Na+、K+、Cl- and metasilicic acid mainly comes from the dissolution of silicate rock, while Ca2+, Mg2+and SO2-4 mainly come from the dissolution of carbonate rock, which is significantly higher than that from the dissolution of evaporite rock. Human activities have a great influence on the chemical characteristics of groundwater. Human activities, such as agricultural planting and aquaculture, generally lead to high NO-3 concentration in water, while human activities aggravate the weathering and dissolution of silicate minerals. The concentration of metasilicate increases. The concentration of metasilic acid in more than 74% of the water samples reached 25 mg/L.