Abstract: Brown tide that occurred in Qinhuangdao coastal waters from 2009 to 2015 caused huge losses of local marine aquaculture and coastal tourism, with devastating effects on marine ecosystems. Nutrients are important biogenic elements for algal growth. It is of great significance to examine the fluctuation characteristics of nutrients in the process of brown tide to understand the nutritional mechanism of brown tide. Based on the survey data of 30 stations located in Qinhuangdao coastal area from April to June 2014, we analyzed nutrient characteristics during the occurrence of brown tide and its relationship with the population dynamics of Aureococcus anophagefferens. The results showed that the concentration of dissolved nitrogen (DN) in April, May and June 2014 was 265.65, 355.36 and 323.71 μg·L^-1 respectively, and the concentration of dissolved organic nitrogen (DON) was 196.98, 242.88 and 177.69 μg·L^-1, accounting for 74.2%, 68.3% and 54.9% of DN, respectively. The concentration of dissolved phosphorus (DP) in April, May and June was 15.95, 11.39 and 11.14 μg·L^-1 respectively. In April and May, PO₄^3--P accounted for a large proportion of the DP, 74.8% and 80.9% respectively. In June, the proportion of PO₄^3--P in DP fell to 33.8%, and the proportion of dissolved organic phosphorus (DOP) in DP rose to 66.2%. The concentration of SiO₃^2--Si in April, May and June was 70.95, 181.13 and 120.68 μg·L^-1, respectively. Except for dissolved inorganic nitrogen (DIN) in May and DON, the distribution of other nutrients had clear characteristics that it decreased gradually from inshore to the offshore, with the relatively high concentrations in river mouth. Through R-factor analysis and nutrient structure analysis, it was found that in April, brown tide was at the development stage, and DOP might be the main driving factor for the growth of A. anophagefferens. In May, brown tide was at the maintenance stage, and water temperature became the main controlling factor. When water temperature was higher than 12 ℃, brown tide could occur. In June, brown tide began to decay, and PO₄^3--P had greater effects on the community structure of phytoplankton. DON was the important factor causing the outbreak of brown tide, with a concentration threshold of 150 μg·L^-1 and the ratio DON/DIN being greater than 1.