Abstract: In order to understand the spatial and temporal distribution patterns of cyanobacterial outbreaks and the effect of exogenous nutrient regulation on cyanobacterial outbreaks in Dianchi Lake, the 3-Dimensional coupled Hydrodynamic-Aquatic Ecosystem Model (AEM3D) from HydroNumerics, Australia was used to simulate the spatial and temporal distribution characteristics of TN, TP and cyanobacteria, and to investigate the response relationship of cyanobacteria under different exogenous nutrient concentrations by regulating the values of exogenous nutrients. The results show that the concentration of TP was higher in spring, which acted as an important nutrient factor in algal growth. The concentration of TN was higher in autumn, which played a key role in algal growth. When simulating single-factor exogenous nutrient reduction at different rates, it was found that total exogenous phosphorus had a greater effect on cyanobacteria than total exogenous nitrogen, while the changes in exogenous nitrogen in spring had a greater effect on cyanobacteria. When only TP was controlled, a 25% reduction was effective in reducing Chl-a concentration in the lake, and when only TN was controlled, a 50% nitrogen reduction was more reasonable. Compared to the reduction of a single nutrient, the effect on control of Chl-a concentration was superior when nitrogen and phosphorus nutrients were both reduced by 10% or above 50% at the same time.