This paper takes the groundwater quality monitoring data in the middle and lower reaches of Dagujia River in Yantai from 1987 to 2017 as the background.Sodium potassium ion, calcium ion, magnesium ion, bicarbonate ion, sulfate ion, chloride ion, nitrate ion and total hardness and salinity are selected as research objects.Grapher software is used to make dynamic graph of groundwater quality and analyze the characteristics of groundwater quality changes over the years.Using AquaChem software rendering Piper trilinear nomograph, summarizes the type of groundwater quality and its change rule.The variation of groundwater quality in the study area in 30 years Is compared and analyzed.Prediction of groundwater quality trend in the middle and lower reaches of Dagujia River by time series analysis.The results show that the main ion concentration of groundwater in the study area is on the rise.The type of water chemistry is changed from HCO3Ca, HCO3·ClCa·Na to HCO3·SO4Ca·Na, HCO3·Cl·SO4Ca·Na, but the quality of groundwater has not changed much.Except the downstream coastal area,most areas have not exceeded Class III water standards,only in some areas, NO3- exceeds the standard.