Abstract:In order to understand the characteristics of phytoplankton community structure in Xisha Xuande Islands, the phytoplankton community composition and environmental factors sampled in February and November 2019 were analyzed. The results showed that 109 species of phytoplankton were found during the two voyages, among which Bacillariophyta were the most with 81 species. The dominant species varied between winter and autumn, Trichodesmium thiebautii, T. erythraeum, Asterionella notata, etc. were the dominant in winter, and did Thalassionema nitzschioides, Leptous danicus and Chaetoceros lorenzianus were in autumn. The average abundance of phytoplankton in winter[(5.27±6.14)×107 cells/L] was significantly higher than that in autumn[(1.56±1.40)×105 cells/L]. The structure of phytoplankton community was mainly affected by nitrite, salinity and other environmental factors. The average of Shannon-Wiener diversity index (H'), Pielou evenness index (J') and Margalef richness index (d') in winter and autumn were 3.15, 0.71, 1.36 and 3.28, 0.75, 1.77, respectively. As a whole, these indicated that phytoplankton community in Xuande Islands had high diversity and rich species, as well as complex and stable community structure in winter and autumn.