Abstract: Waterscape is an important component of landscape architecture. Under the circumstances of water shortage and pollution, along with public increasing awareness of conservation, how to maintain the water quality at a low cost becomes an issue of concern. Landscape water features have the peculiarities of small size, enclosed, sluggish flow, easy to be polluted, etc., which usually lead to eutrophication. The root cause of eutrophication is ecological imbalance, therefore, eco-purification is the preferred method of water purification. Firstly, the aquatic ecosystems in Beijing Olympic Forest Park Lake is simulated with Aquatox, then the ecosystem stability and the effectiveness of existing water purification system are evaluated. Secondly, two adjustments from the perspective of eco-purification, namely using different types of aquatic plants and adding macrobenthos to improve the ecosystem, are presented. Then the two adjustments are simulated individually, and the results are compared to the former. The results show that the existing water purification system and the adjustments are all steady, while the adjustment of adding macrobenthos has the highest fish carrying capacity, and the model without water purification system turns out to be lack of ecosystem stability. The effectiveness rankings are adding macrobenthos > existing water purification system > using different types of aquatic plants > without water purification system.