Abstract: Based on the 6 investigation data of the Dashentang Oyster Reef Marine Special Reserve from 2015 to 2020, we analyzed 18 basic water quality indices, including water temperature, salinity, transparency, pH, dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chemical oxygen demand (COD), oil, heavy metal content, suspended solids and chlorophyll a (Chl a), in addition to the evaluation of the eutrophication index (E), nutrient quality index (NQI) and Nemerow pollution index (P), in order to evaluate the quality of the oyster reef environment in this region. The results showed that the major exceeding standard factors were DIN, DIP, COD, oil and DO according to contribution rate from high to low. The degree of contamination and the main pollutants in seawater showed highly significant annual difference (P<0.001). The N/P ratio of seawater greatly changed from no nitrogen and phosphorus structure limitation to obvious phosphorus limitation. Chl a and primary productivity remained basically stable in this sea area.