Based on the analysis of water samples collected at Sansha Bay during March 30 to April 3, 2016, totally 38 species belonging to 3 phyla and 22 genera were identified, including 34 diatom species belonging to 19 genera, accounting for 89.47% of the total species and it is the main group in the investigated sea area. 3 dinoflagellate species belonging to 2 genera, and 1 chrysophyta species belonging to 1 genus. In spring, the average abundance of phytoplankton was 1.63×10⁵ cells/L. The high value area appears in northwest to Shasha Bay, the Jiaoxi river, Baima port and the waters near the Lumen port. The dominant specie was the Skeletonema costatum, the frequency of occurrence was 100%,but it was mainly distributed in the estuary. The relationship between phytoplankton and environmental factors was studied by Redundancy Analysis(RDA).The results of Redundancy Analysis(RDA) indicated that Dissolved Oxygen (DO),Salinity (SAL), Temperature (T), and Soluble Reactive Phosphorus (SRP),were the most important environmental factors influencing phytoplankton of Sansha Bay in spring.