The study was based on the investigations of fishery resources and environment of Lake Wuli in 2009.Using the Ecopath with Ecosim software beta 6.0, the massbalance of Lake Wuli ecosystem is constructed to analyze the main biomass flows and trophic flows. The model consists of 17 functional groups, which are Large culters, Other piscivorous, Tapertail anchovy, Common carp，Crucian carp, Bighead carp, Other fishes, Silver carp, Herbivorous fishes, Macrocrustaceans, Molluscs, Other benthos, Zooplanktons, Submerged Macrophytes, Other macrophytes, Phytoplanktons, Detritus. Each group represents organisms with a similar role in the food web, and the functional groups cover the main trophic flow in the ecosystem. Through network analysis, the ecosystem of Lake Wuli reached maturity in 2009.Trophic levels of the compartments vary from 1.00 to 3.958 6. The system net work is mapped into a linear food chain and six discrete trophic levels are found with a mean transfer efficiency of 4.4% from detritus and 5.1% from the primary producers within the ecosystem. The geometric mean of the trophic transfer efficiencies is 4.9%. In the course of energy flow, the proportion of total flow originating from detritus is 56%. and that from the primary producers is 44%. The parameters of this ecosystem: Total primary production/total respiration (TPP/TR), Connectance Index (FC), Ascendancy(A), Finn′s cycling index(FC), Finn′s mean path length (FCL)and System Omnivory Index(SOI) are: 1.339, 0.277, 0.267, 0.155, 3.393, 0.119 respectively.