为了深入了解淀山湖夏、秋季浮游植物优势种的生态特征及主要优势种与环境因子的关系，于2012年6月至11月夏、秋两季在淀山湖选取13个点位开展浮游植物群落调查.计算了淀山湖浮游植物优势种的密度、优势度、生态位宽度.共发现淀山湖夏、秋浮游植物群落优势种有4门12属17种.通过将各月均出现的优势种的密度和总密度作Pearson相关来确定对淀山湖浮游植物数量贡献较大的主要优势种，分别为小球藻（Chlorella vulgaris）、尖尾蓝隐藻（Chroomonas acuta）、模糊直链藻（Melosira ambigua）和吻状隐藻（Cryptomonas rostrata）.将4种主要优势种的密度与环境因子作灰关联分析，结果表明，不同季节，影响不同浮游植物密度的关键因子并不相同.夏季，透明度是影响小球藻、模糊直链藻和吻状隐藻密度的关键因子，溶解氧是影响尖尾蓝隐藻密度的关键因子；秋季，总磷是影响小球藻密度的关键因子，溶解氧是影响尖尾蓝隐藻和吻状隐藻密度的关键因子，总氮是影响模糊直链藻密度的关键因子.

In order to understand the ecological characteristics of phytoplankton’s dominant species and their relationships with environmental factors in summer and autumn in Dianshan Lake, a survey was conducted at 13 sampling sites from June to November 2012. The density and dominance and niche breadth were calculated in this study. The phytoplankton dominant species in the Dianshan Lake was composed of 17 species belonging to4 phylum and 12 genera. The density of phytoplankton’s dominant species which appeared every month and the total densityof phytoplankton were analyzed with pearson correlation,and we screened out that  Chlorella vulgaris, Chroomonas acuta, Melosira ambigua and  Cryptomonas rostrata were the main dominant species.The result of grey relationship analysis suggested that different phytoplankton density varied with the change of environmental factors, and the factors which seriously influenced each species were different in summer and autumn. In summer, transparency was the key factor that influenced the density of  Chlorella vulgaris, Melosira ambigua  and Cryptomonas rostrata. Dissolve oxygen wasthe key factor that influenced the density of  Chroomonas acuta.  In autumn, total phosphorus was the key factor that influenced the density of Chlorella vulgaris. Dissolve oxygenwas the key factor that influenced the density of Chroomonas acuta  and Cryptomonas rostrata. Total nitrogen was the key factor that influenced the density of  Melosira ambigua.