Abstract: In recent years, water quality degradation in the Jiangsu coastal waters has led to frequent harmful algal blooms known as the red and green tides. Eutrophication is considered as one of the potential causes. In order to study eutrophication characteristics in this region, the monitored water quality parameters such as dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), and chlorophyll a in 2019 and 2020 were analyzed spatially and integrated as various eutrophication indices. Results indicate that DIN and SRP concentrations in the Jiangsu coastal waters were relatively high nearshore and significantly negatively correlated with salinity. Due to higher precipitation and river runoff, nutrient and chlorophyll a concentrations were higher in summer than in spring and fall, and in the wet (2020) than normal (2019) year. Based on these findings, we conclude that the terrestrial input likely exerts a major control on eutrophication of the Jiangsu coastal sea. Monitoring and load management of the riverine pollution are key to water quality improvement in this region.