Based on data from the aquaculture sea-areas of the middle part of Xiangshan Harbor surveyed in autumn of 2014, and spring, summer, and winter of 2015, nutrient levels and seasonal variation in nutrients were evaluated. The results showed that the inorganic nitrogen and phosphorus levels in autumn were higher than those in spring, summer, and winter. Among all regions, the DIN (Dissolved inorganic nitrogen) concentrations in Ninghai seaweed and Xihu Harbor kelp culture areas were higher than the fourth level of seawater standard (0.50 mg/L), except one sampling station in the winter. PO4-P content were higher than the fourth level of seawater standard (0.045 mg/L) in the spring and autumn. This may be due to human activity, which was focused on the development of local economy and urban upgrading. Additionally, the rivers that flowed through the metropolis around Xiangshan Harbor carried domestic wastewater and rainfall, consisting of superfluous inorganic nitrogen and inorganic phosphorus, to the sea water. Conversely, seaweed, as well as algae such as kelp, was originally cultivated to reduce the level of DIN and PO4-P, and has not functioned optimally during recent years, contradicting with the nutrient data from previous investigation. The N/P ratios of the sea water in the middle areas of Xiangshan Harbor were higher than the Redfield ratio in four seasons, lacking in inorganic phosphorus correspondingly. According to the potential eutrophication assessment model, Xiangshan Harbor possessed potential, rich nutrition, with medium levels of restricted phosphorus in four seasons.