Abstract: To quantitatively evaluate the development and utilization level of coastal areas and the impact of the economic industrial structure of coastal cities on the environmental quality of seawater, the coastal areas of Liaodong Bay were taken as the research object, and the water quality of the coastal waters was evaluated by using the comprehensive water quality evaluation index, Nemero index and principal component index. Based on the analysis of variance decomposition, this paper studied the impact contribution rate of the development and utilization level of the coastal areas, the economic industrial structure and the spatial location on the environmental quality of the seawater. The results showed that the water quality environment of Dalian and Huludao was significantly better than that of Panjin, Yingkou, and Jinzhou near the Liaohe estuary; the marine functional area and seawater quality index had a certain spatial correlation, but the difference between different functional areas was not significant; and the level of sea area development and utilization had an extremely significant positive correlation with the comprehensive evaluation index of sea water quality and Nemeiro index. The per capita GDP of coastal cities and sea water quality index were in an “inverted U-shaped” Kuznets curve relationship; variance decompose analysis showed that the intensity of sea area development and utilization could cumulatively explain 42.3% of the changes in the quality of the seawater environment, the economic and industrial structure could cumulatively explain 31.8% of the changes, the direct impact of the level of development and utilization of the sea area and the economic and industrial structure contributed 16.5%, while the interaction between natural geographic location and sea area development and utilization intensity and economic industrial structure could cumulatively explain 58.9% of the changes. The results of this study strongly support the management and control of sea reclamation, comprehensive management of coastal waters, and optimization of coastal industrial structure, which play an important role in improving the environmental quality of coastal waters.