Abstract: Based on the monitoring data from 2011 to 2018, the trends of inter-annual variations and spatial distribution characteristics of inorganic nitrogen (DIN), active phosphate (DIP), chemical oxygen demand (COD) and petroleum concentrations in Jiulongjiang Estuary were analyzed. The water quality of the area was evaluated and analyzed with fuzzy comprehensive evaluation method. The results showed that the annual average concentrations of DIN and DIP in Jiulongjiang Estuary increased first and then decreased, while the annual average concentrations of COD decreased yearly and the average annual concentrations of petroleum fluctuated. The concentrations of DIN, DIP, COD and petroleum were higher in the southwest than in the northeast of estuary, and they were all affected by the runoff of Jiulong River. The fuzzy comprehensive evaluation showed that the water quality of Jiulongjiang Estuary was under level IV based on the national standard of sea water quality, and the main pollutants were DIN and DIP. The scores of comprehensive evaluation of water quality increased yearly, indicating that water quality tend to improve from 2011 to 2018.