Abstract: Based on the monitoring data of water quality and sediment quality in Luoyuan Bay from 2009 to 2018,the environmental quality in Luoyuan Bay was evaluated according to the nutrition index method and the comprehensive index method of environmental quality classification.The results showed that from 2009 to 2014,the environmental quality of Luoyuan Bay continued to deteriorate.Since 2015,it started to improve.The main problem was that the seawater was seriously polluted,while the DIN and PO₄-P were the principal pollutants affecting the seawater quality over the years.This trend was related to large-scale coastal reclamation in early stage,agglomerated development of port industrial construction and mariculture,and the completion of the retreat of mariculture in late stage.Through analyzing the change trend of environmental quality in Luoyuan Bay in recent ten years,it provided the basis for environmental protection and rational development of Luoyuan Bay.