Abstract: Water qualities by the 4 marine environment graded control areas in Luoyuan Bay was studied based onthe data obtained in May and October 2012.Besides,the horizontal and seasonal distribution of nutrients,ratio ofN/P,and eutrophication status of seawaterwere assessed.The results showed that dissolved inorganic nitrogen(DIN)and active phosphors were important contaminants.The averageconcentrationof DIN was 0.363mg/dm³in May and 0.428 mg/dm³in October while that of active phosphors was 0.039mg/dm³and 0.062 mg/dm³respec-tively.The water quality distrbuted in the same pattem in these two months and it deteriorated from the inlet intothe inner bay.The water quality control objective for fishery environment protection and utilization area in LuoyuanBay was not achieved in both May and October.In case of ecological corridor protection and utilization area inLuoyuan Bay,the water quality control objective was achieved just within the inlet in May,but unrealized withinthe whole bay in October.The situation was somewhat better in the north bank and the ports and industry develop-ment and supervision areas in the south bank.In these two areas,the water quality control objective was achievedin the inlet in both May and October,though it was still unrealized in the inner bay.The water quality was better inMay than in October,but the probability for the outbreak ofred tide was higher in October than in May.Since1980s,the water quality in Luoyuan Bay had deteriorated gradually and it trended to worse especially after 2000.