In order to clarify the characteristics of plankton community structure and understand the current status of water quality in Weishui Reservoir， in this study， plankton and water quality surveys were carried out in the typical area of Weishui Reservoir in July （summer） and November （autumn） 2021， January （winter） and March （spring） 2022. The results showed that there were 75 genera and 129 species of phytoplankton， mainly Chlorophyta， and 23 genera and 31 species of zooplankton （rotifers and planktonic crustaceans）， mainly rotifers. The dominant plankton species mainly included Cyclotella catenate， Scenedesmus biguga， Pseudoanabaena limnetica， Keratella cochlearis， nauplius， etc. The annual mean density and biomass of phytoplankton were 1.656×10⁷ ind./L and 6.32 mg/L， respectively， and the annual density and biomass of zooplankton were 1.75×10² ind./L and 1.92 mg/L， respectively. In terms of spatial distribution， the abundance and biomass of plankton decreased gradually from the upstream channel-type area to the downstream open-water area. Canonical correspondence analysis showed that PO₄^3--P， WT， pH and DO all had important effects on the ecological distribution of plankton communities in Weishui Reservoir， while NO₃^--N and Cond only had an effect on phytoplankton. According to the evaluation of species diversity， the plankton community structure of Weishui Reservoir is relatively stable， and the water quality in the reservoir area is in the mesotrophic status.