Abstract: The spatial-temporal variations and eutrophication of water quality were analyzed based on the monitoring data from Meishan waterway in winter, spring, summer and autumn of 2018. The results showed that NO₃-N was the main component of DIN which accounted for 68.25%～98.21%. The average concentrations of DIN and PO₄-P in winter, spring and autumn were higher than those in summer, but the SiO₃-Si in summer was on the contrary. The concentrations of nutrients were significantly negatively with Chlorophyll a in winter, summer and autumn except summer, indicated that the contents of nutrients were not only affected by phytoplankton consumption, but also by exogenous input and release of environmental media. In addition to summer, the average contents of PO₄-P in the Mangchang Reach were higher than those in the bay, and PO₄-P contents were decreased from the North dyke to the South dyke. The contents of SiO₃-Si in Mangchang Reach were lower than those in the bay in spring and summer, but the autumn and winter were opposite. The assessment by comprehensive pollution index method showed that the Mangchang Reach was mainly moderately polluted and the bay was mainly mildly polluted both in spring and autumn, while opposite in summer. Potential eutrophication evaluation results showed that the water quality of Mangchang Reach possessed moderate restriction of potential eutrophication in phosphorus and oligotrophy, while the bay with potential eutrophication of phosphorus limitation and phosphorus restriction on eutrophication.