A research on phytoplankton community structure of Yangzonghai Lake in 2013 was carried out with the method of biodiversity index. The results show that there are 7 phyla 39 genera of phytoplankton in Yangzonghai Lake, Anabaenopsis sp. and Limnothrix sp. being the dominant species of cyanophyta; and there are 33 species of zooplankton, Rotifera being its dominant species; the Shannon-Weaner index and the evenness index of phytoplankton and zooplankton are 1. 10 ~2. 83 and 0. 37~ 0. 88, respectively, belonging to the state of moderate pollution. The Yangzonghai Lake has been in the nutritional status with the trends of transition to eutrophication.