Dajingshan Reservoir, located in Zhuhai City, South China, is a medium-size water body. It supplies drinking water for the Zhuhai City and Macau in dry seasons. Water is pumped into the reservoir from a nearby river in dry seasons so as to enhance the water storage. Pumped water modified the hydrodynamic processes and ecosystem dynamics. In order to understand the dynamic of rotifer community and the relationships between specific composition of rotifers and the environmental variables, an investigation was conducted monthly in 2005. Altogether 32 species of rotifer were identified, among which 12 species were belonged to Brachionidae, 4 species to Trichocereidae and 4 species to Lecanidae. The majority of the species are tropical or sub-tropical species. Keratella tropica, Trichocerea stylata, Keratella cochlearis, Filinia maior, Anuraeopsis fissa, Brachionus angularis, Brachionus forficula, Ascomorpha ovalis and Collotheca pelagica were the dominant species. They had small body size and lorica. The diversity index of rotifers ranged from 0.29 to 0.8, which were lower than that in Lake Donghu and Lake Xinghu. The abundance and biomass of rotifers ranged from 21 to 1094ind./L and from 4.04 to 1127μg/L, respectively. The maximal abundance and biomass occurred in February and May, respectively. The body length of rotifers ranged from 50μm to 620μm. The total abundance of rotifers was contributed by of small-sized species with a body size less than 200μm, while the rotifers biomass was dominated by medium-sized species with body size from 200-400μm. Secchi disk depth, temperature, total phytoplankton biomass and Cyanophyta biomass were the main factors affecting the species composition and quantitative dynamics of the rotifer community.