β diversity refers to the spatial variation of species composition, and its pattern and the potentially driving factors are important issues of understanding biodiversity. In the present study, we seansonlly investigated benthic diatoms in a subtropical medium river- Liuxihe River in southern China, Guanggzhou, Guangdong Province. In Baselga's framework partitioning β diversity, the Sørensen dissimilarities among sampling sites were decomposed into two complementary components:species turnover and nestedness. The relative importance of environmental and spatial processes on β diversity and its components were explored by using generalized dissimilarity modelling (GDM). The results showed that β diversity, and its two components:species turnover and nestedness had no significant seasonality. β diversity was dominated by species turnover (>75%) in all the four investigated seasons. Both environmental selection and spatial process shaped the β diversity and its turnover component in Liuxihe River. Environmental selection plays a major role in influencing the β diversity and its turnover component. The importance of dispersal limitation increased in the dry season compared to that in the wet season. As a distance-based nonlinear regression method, GDM well identified the community variation of benthic diatoms (i.e., β diversity) and its two complementary components along both spatial and environmental gradients.