Abstract�� Through the investigation in May and September, the Phytoplankton species composition��quantity distribution��diversity index in Yueqing Bay was researched The results showed that there were 5 phylum 37 genuses 62 species in May and there were 5 phylum 43 genuses74 species in September. The Phytoplankton were composed of Diatom and Dinoflagellate. Diatom was absolute predominance judged from species and abundances. The Dominant species of May were Skeletonema costatume and Coscinodiscus jonesianus, and the Dominant species of September were Skeletonema costatume and Planktoniella blanda. The Cells number of phytoplankton assemblage of Septmber were more than May of 16 sites, but the distribution quite of May was even than September. the Shannon-Weiner diversity index��Margalef richness index and Simpson dominance index of September were more than the May, but the Pielou evenness index was less than than the May. Through the study of the Zooplankton species composition��quantity distribution��diversity and relationship between abundance and environmental factors in Yueqing Bay is to provide evidence for ecological monitoring, evaluation, and provide scientific evidence for the development of the sustainable utilization of marine resources to the sea.