Rotifers, the most diverse group of zooplankton in freshwater ecosystems, play an important role in structuring food webs. As many rotifers are sensitive to environmental changes, their communities change rapidly with alternated environments and are well understood from a niche perspective. The functional traits of species generally provide more information on ecological adaptation in the community assembly. Among functional traits of rotifers, body size, trophi, defensing structure and defensive behaviors indicate rotifers' abilities to use food and coping with their predators. To understand the structure and assembly of rotifer communities in (sub)tropical reservoirs in spring when both food and predation pressure increase, we investigated the pelagic rotifers of 43 reservoirs in southern China from March to May of 2018. Physicochemical variables of water bodies were measured, including water temperature, water depth, water transparency and chlorophyll-a concentration. A total of 45 species were identified from all the pelagic samples, and most species were from Trichocerca (10 species) and Brachionus (7 species). Rotifer communities were dominated by small-sized species (83.11% in total abundance and 53.10% in total biomass). Rotifers with trophi of malleate and virgate dominated in all the trophi types (≥ 90%), while those species with lorica and spine (66.59%) dominated for defensive structure. Such a pattern for species composition and functional structure demonstrates adaptation of rotifers in warmer waters with high temperature and high predation pressure. Redundancy analysis showed that food resource, water temperature and competition are the main factors structuring significantly the rotifers communities in our investigated reservoirs.