In order to improve the water quality of Yuncheng Nanhu Lake in Heze City, Shandong Province, according to the current conditions of Nanhu Lake, the total annual pollution load into the lake was quantitatively calculated. Combined with the decontamination capacity of common water purification plants and animals investigated in the literature, a comprehensive water purification scheme of Nanhu Lake based on water ecosystem balance was designed with the goal of class Ⅳ water in the surface water environment quality standard. In the scheme, the planting area of aquatic plants such as reeds, lotus, yellow calamus and so on was calculated based on the pollution load into the lake. The ecological floating islands were laid out based on the distribution of nitrogen concentration field simulated by MIKE21. Suitable stocking species and quantity of aquatic animals(fish and benthic animals)were proposed. According to the designed water purification scheme, the conclusion is estimated that in the future, the water quality of the lake can reach class Ⅳ except for COD indicators. COD mainly comes from tourism pollution. Therefore, the control of tourism pollution is very important to ensure the water quality of the lake area.