Qinzhou Bay (108.46-108.75°E, 21.54-21.87°N), located at the middle coast of Guangxi Province, is a semi\enclosed lageniform bay. As one of the most important marine economic bases on the south coast of China, Qinzhou Bay plays a significant role in numerous marine industries, which involve port transportation, coastal tourism, and marine aquaculture and fisheries, among others.In recent years, along with rapid economic development and a denser human population, many environmental problems have arisen and seriously threaten both the marine ecosystem and economic sustainable development, such as eutrophication, red tides, and the decrease of coastal wetlands, among others.Phytoplankton, as is well known, is very sensitive to regional environmental change and plays a key role as a primary producer in the marine ecosystem.However,there is little research regarding the effects of variable environmental factors on phytoplankton communities in Qinzhou Bay.In 2013, to determine the relationship between marine exploitation and phytoplankton communities, we conducted a spring (March) and summer (July) survey in Qinzhou Bay. Cluster and canonical correspondence analysis (CCA) were applied. The results were as follows:3 phyla, 45 genera, and 115 species were classified during the entire year in Qinzhou Bay, including 100 diatom species, 14 dinoflagellate species, and 1 cyanobacteria species.The warm water species dominated phytoplankton communities in both spring and summer, although we observed a substantial change in community structure between the seasons. The results of CCA showed that suspended substance, pH, salinity, and nutrients were the main environmental factors that affected the distribution of phytoplankton. Under the influence of different runoff and water mass, most of the phytoplankton communities in spring were easily clustered into similar communities; however, those in summer tended to be more varied.