Based on the data of lake survey conducted during 2007—2010,an mass-balanced ecosystem model of Lake Chaohu was constructed using Ecopath with Ecosim 6.1,with the aim of characterizing its ecosystem structure and functioning,which would help making ecosystem-based management.The model comprised 16 functional groups including primary producers,the main species of fishes,non-fish vertebrates,and detritus.Results showed that the functional groups are organized into four trophic levels.The system throughout,production and consumption are relatively large,with the values of 41 003.08,17 937.42 and 4 486.67 t/(km²·a),respectively.Flows from trophic Ⅱ and Ⅲ dominated the ecosystem.Considering Odum's theory of ecosystem development,Lake Chaohu was placed on a low developmental stage with higher net primary production(NPP),total primary production/total respiration(TPP/R)and lower connectance index(CI),system omnivory index(SOI),Finn's cycling index(FCI)and Finn's mean path length(FMPL).The cause of the degeneration of Lake Chaohu ecosystem was considered to be the high biomass and production of primary producer,phytoplankton and its low rate of utilization.