By setting a total of 6 sampling stations, Yongzhou, Hengyang, Zhuzhou, Xiangtan, Changsha, Yueyang, and 35 sampling points, we investigated the species composition, dominant population, density distribution and community structure of phytoplankton in Xiangjiang River of Hunan Province, and analyzed the phytoplankton species, biological index and their correlation with environmental factors during April 2020 to January 2021. The results showed that 259 species of 133 genera were identified in the studied area including 92 species of Chlorophyta and 71 species of Bacillariophyta, accounting for 35.52% and 27.41% of the total species, respectively. The phytoplankton density of Chlorophyta and Bacillariophyta reached 1.00×104 ind/L and 6.20×103 ind/L, accounting for 47.39% and 29.38%. The Xiangjiang River was Chlorophyta-Bacillariophyta type of water body. The overall phytoplankton species increased gradually over winter, spring, summer and autumn. In spring and winter, it was mainly Bacillariophyta water, and in summer and autumn, it was mainly Chlorophyta water. Densities of phytoplankton were ranged from 6.2×103 ind/L to 1.00×104 ind/L, average density of 2.11×104 ind/L in four seasons. The most maximum density was in autumn, and the most minimum density was in spring. Except for the maximum density of Hengyang station in summer, autumn was the season for getting maximum density in other sampling stations. A total of 13 dominant phytoplankton species appeared in the four seasons, and the dominant species of phytoplankton was mainly Chlorella vulgaris. The annual average values of phytoplankton α-diversity index(H), richness index(D), and evenness index(J) were 3.20-4.80, 1.13-4.79, 0.73-0.81, respectively. H and D increased successively in Winter, Spring, Summer and Autumn, and the seasonal difference in J was not obvious, but the quarterly change of D was large. Among the 6 sampling stations, the H, D, J annual average of Zhuzhou station were the lowest; Yongzhou station had the highest H; Hengyang station had the highest D value, Yongzhou station was the second; Yongzhou station and Xiangtan station had the highest J. It could be seen that the Xiangjiang River water was in a good quality with slight pollution, and the upstream water quality was better than that of the downstream. Correlation analysis found that the phytoplankton community distribution was somewhat correlated with environmental factors such as dissolved oxygen, pH and nutrient salt.