Lake Xingkai is suffering from eutrophication and frequent algae blooms.Based on the DELFT-3D model,this study established a set of parameters applicable for the Lake Xingkai ecosystem and simulated the dynamics of water quality and algae.In addition,this paper simulated the change of water quality and algae by setting different control scenarios.The results show that the concentrations of TN,TP and Chl.a rose rapidly in the small Lake Xingkai.With the initial value of 8.96 mg/m³,the Chl.a was increased by 32.37% and 65.51% in 2015 and 2020,respectively,which would lead to serious risk of algae bloom especially in May and August.The simulation result revealed that the concentration of Chl.a changed significantly with the amount of nitrogen input in the small Lake Xingkai.With further nutrient-cutting efforts,the water quality of the small Lake Xingkai could reach type Ⅱ water,the water of the large Lake Xingkai could reach type Ⅲ water.The small Lake Xingkai plays a role of buffer zone for the large Lake Xingkai.Chl.a should be added to the eutrophication control standards to provide early warning for algal bloom.