This study was conducted to monitor and analyze the water quality and the dynamic changes of phytoplankton in the closed aquaculture area of Bihai Jinsha in Fengxian of Shanghai were monitored and analyzed and the pollution and potential risks during the aquaculture process was analyzed. The investigations took place in April, July, October 2016 and January 2017. Water quality surveys showed that DIP, DIN and COD concentration remained relatively high in April, July and October. Among them, DIP and DIN concentrations were highest in April, while the highest values of COD concentrations occurred in July. From October to January, the water quality improved significantly at the end of the cultivation. Phytoplankton was found to have a total of 42 species of 7 Phyla, of which most were in autumn and summer and it showed obvious four-season succession. The species with the highest dominance in the four seasons were Chroomonas acuta, Chlorella, Anabaena circin alis and Oscillatoria, and it is worth noting that Chlorella is a dominant species in all seasons. The high abundance of phytoplankton is focused on the summer and autumn. The Shannon-Wiener diversity index (H') and evenness index (J) were from 0.709 to 2.088 and from 0.440 4 to 0.870 7 respectively. The analysis showed that the stability of the community structure of phytoplankton was poor and the water pollution was heavy. The environmental factors affecting the abundance of phytoplankton were nutrition concentration and temperature, and the dominance of Anabaena circinalis and Skeletonema costatum were higher in autumn and both in summer and autumn, respectively, which may cause the risk of red tide. It is necessary to control the aquaculture capacity, improve water quality, and optimize breeding environment.