Abstract: The species of phytoplankton in typical rivers and reservoirs in Xinzhou City of Shanxi Province in autumn of 2020 were investigated, and their diversity was analyzed. The results revealed that in total 111 species and 8 phyla existed in rivers while 125 species and 8 phyla were found in reservoirs, providing the cell densities ranging within （0.009~13.110） ×10⁶ cells/L, along with an average density of 3.299×10⁶ cells/L in rivers, and the counterparts for reservoirs were（0.205~17.310）×10⁶ cells/L and 6.526×10⁶ cells/L respectively. As estimated, the universal dominant species in the sampling sites which represented the related drainage basin included Anabaena oscillarioides, Pseudanabaena sp., Chroomonas acuta, Chroomonas acuta, Synedra acus, Navicula capitatoradiata, Raphidiopsis sinensia, and Diatoma vulgare var. vulgure. It was concluded that the biomass and cell density of phytoplankton were spatially unevenly distributed as well. According to Shannon-Wiener diversity index, Pielou uniformity index and Margalef richness index applied to calculate the overall phytoplankton diversity index of Xinzhou City, the phytoplankton resources in the reservoirs were basically abundant, the structure was practically stable, and the biodiversity was better than that of the rivers. The water quality of 22 sampling sites was mainly in the state of mild and moderate pollution.

Key words: phytoplankton, community structure, diversity, Xinzhou City