In order to investigate the streamwise variation of zoobenthos communities along the river in wet and dry seasons under the influence of cascade reservoirs, sampling processing and metrological identification were carried out in wet season(August)and dry season(January)along Nandujiang River in Hainan Province, which is a large tropic river in China. The biomass, abundance, diversity and uniformity of zoobenthos were analyzed. The results show that there are 22 species of zoobenthos in 4 classes, 2 phyla in wet and dry seasons. The abundance of each species ranges from 0 to 236 ind/m², and the biomass ranges from 0.27g/m² to 31.5g/m². The streamwise variation of zoobenthos communities along main stream of Nandujiang River is greatly influenced by the cascade hydropower constructions. Water discharges in wet and dry seasons have significant influence on zoobenthos communities. Influenced by the water storage in reservoirs and the corresponding change of hydraulic connectivity during the dry season, the streamwise variation amplitude of zoobenthos in dry season is larger than that in wet season. Unlike temperate rivers, most of the zoobenthos in the main stream of Nandujiang River can reproduce well in winter, and the abundance and biomass of zoobenthos in dry season are larger than those in wet season.