Abstract: In order to understand the temporal and spatial succession characteristics of the plankton community structure and water quality in Shuitou reservoir, Yashui town, Guizhou province, a comprehensive survey of water quality and plankton in Shuitou reservoir werelaunched in December 2018 and March 2019. During the study period, a total of 69 species of phytoplankton in 57 genera（including variants） were detected in 7 phyla. Among them, 49 species of phytoplankton in 7 phyla and 46 genera were detected in winter, and 34 species in 29 genera and 5 phyla were found in spring. Chlorophyta and Bacillariophyta were dominant groups. The average density and average biomass of phytoplankton in winter were 5.98×10~4 ind/L and 83.32×10^-3 mg/L, respectively; the average density and average biomass of phytoplankton in spring are 14.39×10~4 ind/L and 64.70×10^-3 mg/L, respectively. A total of 26 species of zooplankton were identified in 3 phyla, including 8 species of rotifer, 11 species of cladoceran, and 7 species of copepod. The average density and average biomass of zooplankton in winter were 14.40×10~2 ind/L and 62.20 mg/L; the average density and average biomass of zooplankton in spring were 17.55×10~2 ind/L and 55.55 mg/L, respectively. Results of plankton biodiversity showed that Shuitou reservoir belonged to moderate pollution during the survey period, but the water quality of some sampling points had a tendency to deteriorate. The evaluation results corresponded to the analysis results of water quality and hydration characteristics. This study reveals the plankton community structure of Shuitou reservoir in Yashui town, and evaluates its water quality, so as to provide basic information for the current situation of the water ecological environment and water source protection measures in the area.