The plankton composition and distribution were investigated in Xinfengjiang reservoir in flood and dry seasons of 2000. It was oligotrophic with low density and richness of phytoplankton and zooplankton. 34 species of phytoplankton and 22 species of zooplankton were observed in the reservoir, but fluctuated seasonally. Phytoplankton was predominated numerically by Cyanophyta and Chlorophyta which were 31.7% and 26.8% of the total amount respectively in the flood season and then by Bacillariophyta with 63.9%. In the dry season, Keratellca cochlearis predominated numerically in the flood season and then Mesocyclops leuckarti and its copedid and nauplii in the dry season, and though the abundance of zooplankton was a little higher in flood season than in dry season, the biomass was much higher in the dry season than in the flood season.