Abstract: In order to reveal the community structure characteristics of plankton in cascade reservoir of Jialing River, the field acquisition of the plankton in 12 reservoirs of Jialing River in Sichuan stream segment has been conducted in both dry and rainy seasons. The community structure characteristics of plankton were investigated, the Shannon-wiener diversity index, the Margalef richness index、the Pielou evenness index and the Simpson diversity index have been adopted to assess the water quality through combining with the indicator species in dominant species.Results show that the phytoplankton is collected with a total number of 8 divisions, 42 families, 95 genera and 171 species (including varieties),The numbers of species in Bacillariophyta, Chlorophyta and Cyanophyta were richer than others. The collected zooplankton includes a total of 4 classes, 9 orders, 21 families, 30 genera and 62 species, which respectively belong to the protozoa,pseudocoelomata and arthropoda, and there are 21 kinds of dominant groups. Plankton evaluation results determine the water quality belong to the moderate polluted state.