Abstract: According to the survey data of phytoplankton in spring, summer, autumn and winter from 1998 to 1999 in the West Guangdong Waters, the main species composition and the characteristic of the community structure of phytoplankton in the waters was studied based on the method of multivariate analysis such as the principal components analysis and the hierarchical cluster analysis. Altogether 267 species of phytoplankton were identified in the survey, which ascribed to 5 phyla of Bacillariophyta, Pyrrophyta, Cyanophyta, Chlorophyta and Chrysophyta. Bacillariophyta was the most with the species of 182 (68. 2 %), and followed by Pyrrophyta with the species of 75 (28.1 %).In the principal components analysis, 3 principal components were picked up with the accumulated contribution rate up to 100 %. The result showed that the species, such as Skeletonema costatum, Thalassiothrix frauenfeldii, Navicula subminuscula,Oscillatoria sp., Thalassionema nitzschioides, Thalassiosira subtilis, Chaetoceros denticulatus, Lauderia borealis, Biddulphia sinensis, Ceratium fusus, Rhizosolenia alata, Rhizosolenia stolterforthii,Eucampia zoodiacus, Rhizosolenia styliformis and Chaetoceros pseudocurvisetus, composed of the principal components of phytoplankton in the waters.Using the hierarchical cluster analysis, the species of phytoplankton in the waters were divided into 2 community groups in 3 seasons of spring, summer and autumn, one was the inshore group and the other was the offshore group. While in winter the differentiation of community group was unobvious. The seasonal successions of the various main species were quite obvious. Skeletonema costatum, Navicula subminuscula,Thalassionema nitzschioides and Thalassiosira subtilis dominated the species in quantity in spring, summer, autumn and winter,respectively. While the fresh water species, Oscillatoria sp., was also identified with a large amount in summer.