Abstract: A study on community st ructure of zooplankton , including density diversity and biomass di2 versity , was carried out f rom J an. to Dec. of 1999 in Lake Qiandaohu , Zhejiang. The diversity index of rotifers was the highest observed. The result s show that the higher the t rophic level of the lake , the higher the density diversity index of rotifers in definite t rophic level range (f rom oligot rophic to mesot rophic) . Regression analysis among the two zooplankton diversity indices and community factor under variations in time and space demonst rate the following relationships : Monthly variation 　density diversity = - 0. 922 + 4. 521density evenness 　n = 12 , r = 0. 872 , p < 0. 001 biomass diversity = 1. 99 - 0. 348 Daphnia hyalina biomass 　n = 12 , r = - 0. 868 , p < 0. 01 Horizontal variation 　density diversity = 2. 35 + 0. 008 species number 　n = 10 , r = 0. 672 , p < 0. 05 biomass diversity = 2. 88 - 1. 739 biomass dominance 　n = 10 , r = - 0. 826 , p < 0. 01