Abstract: To find out the community structure characteristics and seasonal succession of dominant species in Changhu Lake, phytoplankton and environmental factors were investigated from April, 2015 to January, 2016. The results showed that 14 dominant species of phytoplankton were identified and Cyclotella comta, Chlorella vulgaris and Euglena acus were common species in the all seasons. Niche indexes and the characteristics of the community structure of dominant species were analyzed. The niche breadth index varied from 1.002 to 2.377 for Chlorella vulgaris in summer. Wide niche breadth species, such as Chlorella vulgaris, Cyclotella comta and Oscillatoria amphibian, were considered common indicator species in eutrophic water. The other indexes, such as the outlying mean index (OMI) (0.25—3.71), tolerance index (TOI) (0.13—3.35) and niche overlaps (0.02—0.93), were determined. The correlation between 7 environmental parameters and dominant species analyzed by canonical correspondence analysis (CCA) showed that there were significant positive correlations between the TN, TP and several dominant species, such as Merismopedia.tenuissima, Oscillatoria amphibian, Scenedesmus quadricauda, Cyclotella comta and Euglena acus, in summer. Comprehensive analysis showed that the characteristics of community and niches were significantly correlated with the morphology, lifestyle and habitat of dominant species of phytoplankton. There were also different abilities to utilize the habitat resources of dominant species in each season. Compared with the date in 2012, Gymnodinium aeruginosum was considered a dominant species in winter, and the density increased. The number of wide niche breadth species increased at the same time. The results showed that Changhu Lake remaind in the eutrophic state and that the degree of eutrophication tended to increase.