Dabokou is located in the south of Caohai, Lake Dianchi, with an area of 0.52 km² and an average water depth of about 2 m. As a typical severely eutrophic lake, Dabokou has undergone two phases of ecological restoration in 2015 and 2019. In recent years, the effects of the restoration have begun to be seen. In order to analyse and explore the reasons for the improvement of water quality and ecosystem in the successful restoration waters, this study selected the continuous monitoring data from February 2015 to December 2021 and divided Dabokou into four parts from A1 to A4 according to the engineering situation and water ecological situation. Firstly, the change trends and correlations of suspended solids (SS), chemical oxygen demand (COD_Cr), total phosphorus (TP), total nitrogen (TN) and chlorophyll-a (Chl.a) in the four areas were analysed. Secondly, the restoration effects of different ecological projects were investigated. Finally, the restoration effects of Dabokou were analysed by comparing with Caohai and Waihai. The results showed that after treatment, COD_Cr, TP and Chl.a decreased stably from A1 to A4 area. COD_Cr decreased by 18.65, 27.96, 25.26, 40.92 mg/L; TP decreased by 0.11, 0.10, 0.11, 0.14 mg/L; Chl.a decreased by 0.037, 0.068, 0.067, 0.106 mg/L, respectively. SS showed strong seasonal variations and TN showed a continuous decreasing trend only in area A4, the south-eastern part of Dabokou, with a decrease of 0.68 mg/L. Correlation analysis showed that COD_Cr and TP had the strongest correlation with Chl.a, which could be the key factors affecting algal growth. The water diversion and exchange project reduced nutrient concentrations and accelerated water circulation, and the microfilter cleaning and algae removal project reduced algal biomass and the risk of algal pollution. And through the purification functions of submerged macrophytes, the plant restoration project provided conditions for the formation of the macrophyte-dominated state lake. It is considered that the plant restoration project is the most direct, economical and long-term measure among the above projects. Comparing Dabokou with Caohai and Waihai, it can be concluded that under the same geographical and climatic conditions, the ecological restoration of the south-eastern water of Dabokou has achieved some success. Overall, the Dabokou area, as a case of successful restoration of the severely eutrophic, algae-stable state lake, its experience has important reference value for the further ecological environment restoration of Dabokou itself, Caohai and even the whole of Lake Dianchi.