Abstract: Variations of phytoplankton community structure in Dangbi Town of Xingkai Lake was investigated in July 2009.The results showed that the phytoplankton assemblage was composed of 41 species in total,belonging to seven taxonomic groups.Chlorophyta were represented by the highest percentage of taxa(39.0%) followed by Bacillariophyta(24.4%).The average cell density of phytoplankton was 192.97×104ind·L-1 and the average biomass was 2.4605mg·L-1.Bacillariophyta were represented by the highest cell density(147.47×104ind·L-1) and biomass(2.2818mg·L-1).Dominant species concluded Bacillariophyta,Chlorophyta,Cyanophyta,Xanthophyta.Dominant species were Cyclotella comta,Melosira granulate,Chlorella vulgaris,Ocystis lacustris,Chroococcus minor and Tribonemn sp...The diversity of phytoplankton in that lake was abundant(the value of H’ was 2.09;the value of J was 0.56).Over time,there was little change in dominant species and large change in species composition,cell density and biomass.The later time was the lower X index was.Compared with data between 2001 and 2009,species composition and cell density of phytoplankton in Xingkai Lake declined slightly.Dominant species of Bacillariophyta and Cryptophyta declined and dominant species of Chlorophyta increased.The percentage of filamentous algae in dominant species was increasing.In addition,the biomass of phytoplankton rose in Xingkai Lake.At the same time,fish production potential tended to increase in Dangbi Town of Xingkai Lake.There were two purposes of this study.One purpose was to accumulate basic data of phytoplankton resources in Dangbi Town of Xingkai Lake.The other purpose was to provide reference data for fish feeding habits that was studied by co-workers in Xingkai Lake.

Key words: Xingkai Lake, Phytoplankton, Phytoplankton community structure