Abstract: Based on the data of lake survey conducted during 2008-2009 and the published data of the trophic ecology of key species, the exploited freshwater ecosystem of Lake Taihu was described using Ecopath with Ecosim 6.1 with the aim of characterizing its functioning and structure. The model comprised 20 functional groups including primary producers, the main species of fishes, nonfish vertebrates, and detritus. Results showed that the functional groups were organized into four aggregated trophic levels with the highest levels corresponding to the top predators, culters. Two trophic pathways were found in Lake Taihu, the detrital pathway and grazing pathway. The detrital pathway dominated in the ecosystem. As a consequence of the low ecotrophic efficiency of primary producer and detritus (trophic level Ⅰ), the accumulating detrital sediments continually released waste nutrients back into the system, resulting in its internal pollution. Considering Odum and Ulanowicz’s theory of ecosystem development, the ecosystem was placed on a low developmental stage with high net primary production (NPP), net primary production/total respiration (NPP/R) and lower connectance index (CI), system omnivory index (SOI), and Finn’s cycling index (FCI). The results of mixed trophic impacts and keystone species selection showed that the increasingly intensive fishing exerted a negative effect on the ecosystem, and the topdown effects of top predators were becoming much obviously reduced.