Yangcheng Lake is the third largest freshwater lake of Taihu basin, which is an important water source of the Suzhou area and the only preparing source of drinking water for the city of Kunshan. Yangcheng Lake plays an important role in domestic water, industrial water, and irrigation and fisheries resources. Since 1980s, with the further use of the water resources in Yangcheng Lake, the nutrients were gradually enriched in the lake, which accelerated the eutrophication process of the lake. Algal blooms outbursted in Taihu Lake and other lakes in 2007, and all sectors of society attach great importance to the safety problems of water environment in recent years. Yangcheng Lake which is famous for culturing high quality crab (Eriocheir sinensi) had a large area about 5 400 hm² for the purse seine aquaculture. In order to protect the ecological environment and the source of drinking water ,the government decided to reduce the area to about 2 133 hm² in 2008. We conducted a research about crustacean zooplankton’s community structure, temporal changes and their relationship with environmental factors in Yangcheng Lake, and analyzed the differences inside and outside of the pen about the crustacean zooplankton with a purpose to reveal whether the crustacean zooplankton of Yangcheng Lake has a response to the pen. We also accumulate data for the aquatic ecosystem variation of Yangcheng Lake and provide a theoretical basis for the sustainable development of the ecological fishery. The main physical and chemical characters (TP, TN, SD and Chl.a), species composition, density, biomass and the diversity index inside the pen were not significantly different from those outside the pen（P>0.05）.