Abstract: Based on the water quality monitoring data and zooplankton survey data of 8 state-controlledmonitoring points in Chaohu Lake area,the diversity index of the zooplankton community structure wasanalyzed and the water quality was assessed. The zooplankton density was also analyzed with cluster a-nalysis method. The results showed that 41 species ( genera) of zooplankton were identified in three in-vestigations,and rotifers,cladocerans and copepods were the main groups. The Shannon -Wienerdiversity index in the monitoring points of Chaohu Lake did not change significantly. The Margalef rich-ness index was greater in 2020 than that in 2019,greater in the spring than that in the autumn,andslightly greater in the eastern lake than that in the western lake. Combined with the results of zooplank-ton diversity index analysis,water quality physical and chemical factors assessment,it was concludedthat the water quality of Chaohu Lake was in the state of mild-moderate pollution. The cluster analysisresults showed that the water quality and zooplankton community structure in the monitoring points,ex-cept the middle monitoring point of eastern lake,had little difference. Close-