During January 2006 to December 2007,phytoplankton and environmental factors were monitored for twenty times inFuchunjiang Reservoir. A total of 10⁷ taxi were identified by microscope. 1'he phytoplankton density was ranged from 0. 21/10⁵-3.01× 10⁷cells/L.The specific composition of phytoplankton community changed with the seasons. Bacillariophyta, Chlorophytaand Cryptophyta dominated in Spring; Cyanophyta and Bacillariophyta dominated in Summer; and Bacillariophyta and Cryptophytadominated in Autumn and Winter.The structure of phytoplankton community was obviously affected by hydrological conditions.There was significant positive correlation between phytoplankton density and water temperature. The correlation coefficients betweenphytoplankton density and transparency, TN, TP varied in different ranges. Phytoplankton density was significant positive correlationswith water temperature, TN/TP, and soluble silicon. TN and TP concentrations were high enough to meet the needs of algal growth.Low N/P between 8 to 30 showed that nitrogen and phosphorus content may not be limiting factors for the growth of algae in Fuchun-jiang Reservoir. The seasonal change of phytoplankton community and density were obviously affected by seasonal change in hydrolog-ical,especially by precipitation, water temperature and water retention time.