This paper presents an ecological-economic model for a lake and its watershed systems. We describe the linkage between the watershed system and the lake aquatic ecosystem and the modeling process. The lake-watershed system was divided into six subsystems: social system, economic system, terrestrial ecosystem, lake water system, pollutant system, and lake aquatic ecosystem. The model equations were constructed based on five main assumptions. The Lake Qionghai watershed in southwestern China, which is undergoing rapid eutrophication, was used as a case study. The targeted goals for total phosphorus (TP) and chlorophyll a (Chl a) concentrations in the lake in 2015 are 0.025 and 10.0 mgm 3, respectively. We present two scenarios from 2004 to 2015 based on the ecological-economic model. In both scenarios, the TP and Chl a concentrations in the lake are predicted to increase under the effects of watershed pressures and the targeted goals cannot be met. The application of techniques to reduce pollutants loading and the corresponding pollutants reductions are reflected again in the constructed model. The model predicts that TP and Chl a concentrations will decrease to 0.024 and 7.71mgm3, respectively, which meet the targeted thresholds. The model results provide directions for local government management of watersheds and lake aquatic ecosystem restoration.