Abstract:Base on the zooplankton samples collected in two cruises for studying the change tendency of ecological environment in the Beibu Gulf, planktonic Ostr- acoda communities in autumn and winter in the Beibu Gulf were investigated by multivariate analysis. A total of 11 planktonic Ostracoda species were identified and grouped into three ecotypes, i.e., Huposaline and warm-water group, Eurythermal and eurysaline group, as well as Hyperthermal and hysaline group. The average abundance of all species was low, and Euconchoecia aculeate was the most abundant one. Based on the cluster analysis and multidimensional scaling analysis,planktonic Ostracoda in the Beibu Gulf was a community of stable structure, while in autumn and winter, the community also could be divided into two different sub-communities. To understand the relationship between the community structure and the environmental factors, correlation coefficients for the abundance and the environmental factors were calculated. It indicated that water temperature and salinity had tiny impact on planktonic Ostracoda communities, but there was some rule in its change rhythms. Sub- water temperature and salinity had strong impact on community Ⅱ in winter.