Abstract:A multidisciplinary study on netz\|phytoplankton community was carried out in Changjiang (Yangtze) River Estuary and adjacent waters February to November, 2006. In total, 5 phyla, including 72 genera and 177 species were identified (including uncertain species), of which chain\|shaped ones were dominant, in which diatoms dominated, and dinoflagellates went the second place. Species of Chlorophyta, Cyanophyta and Chrysophyta, were also found. Skeletonema costatum prevailed cross\|season in the whole investigation period, while some others, seasonally, such as Noctiluca scientillans and Prorocentrum dentatum in spring, Proboscia alata f. gracillima in summer, Coscinodiscus jonesianus in autumn, and Coscinodiscus asteromphalus in winter. In the study areas, temperate coastal species were the major ecotype, while warm water species and oceanic species were occasional. Cell abundance decreased in turn from summer, spring, winter, to autumn, in average values of summer and autumn at 2027.41×104 and 22.15×104 cells m-3, respectively. The species composition, abundance and diversity varied clearly in spatial and temporal dimensions. The variation patterns of cell abundance are largely consistent with those shown by historical data, except for certain cases. Change in annual runoff of the river is believed responsible for the variations.