Abstract: Marine environmental quality assessment is the basis of marine environmental management, and its accuracy depends on the level of marine environmental monitoring and evaluation. In order to establish a scientific and effective indicator evaluation system and analyze the current seawater quality situation in western Daya Bay accurately, we carried out an exploration and research on sea water quality assessment in Daya Bay nuclear power sea area by improving grey relational degree clustering and combining it with hierarchical clustering. The evaluation results show that for relative evaluation of seawater quality, the proportions of Class I, Class II and Class III stations were 20.83%, 66.67% and 12.5%, respectively, which was an overall good result. Comparing the the four seasons, it is found that the average absolute correlation followed a descending order of summer (0.747 9) > winter (0.734 5) > spring (0.729 0) > autumn (0.709 7). The seawater quality was better in summer but worse in autumn. According to the evaluation results, the 24 stations in Daya Bay can be divided into three areas, which is consistent with the actual production, living conditions around Daya Bay and field survey, proving the operability of this evaluation method.