Phytoplankton and environmental factors at the estuary of Maixi River in Baihua Reservoir were investigated monthly from July 2009 to June 2010.Results showed that there were 66 species(genus),which were mainly composed of the chlorophyta,ba-cillariophyta and cyanobacteria.The phytoplankton community was dominated by Pseudanabaena limnetica in summer and fall and by Cyclotella meneghiniana in winter and spring.The abundance of phytoplankton ranged from 1.17×10⁴ to 3.35×10⁷ cells/L.The minimum phytoplankton abundance occurred in April of 2010,and the maximum occurred in July of 2009.The phytoplankton abundance composition was dominated mainly by cyanobacteria from April to September, but by bacillariophyta and pyrrophyta from October to March.Canonical correspondence analysis showed that temperature was the most important driving factor in regulating the composition and feature of phytoplankton community at the estuary.Nitrogen and phosphorus were the second important driving factors for the structure of phytoplankton community.Euglenophyta and a majority of cyanobacteria were affected by water tempera-ture and turbidity,but chlorophyta and bacillariophyta were affected by the concentrations of nitrogen and phosphorus among these environmental factors.