Aiming at the eutrophication state of Dian Lake, based on hydrodynamics principle, and some available information about Dian Lake, such as eco-environmental construction planning, the previous work, and so on, a vertical-averaged 2-D hydrodynamic model of ecosystem is established under combination of wetland plants, bed mud, and water change. The model is applied to simulate flow and concentration fields of present lake water, and lake waters after breakwater removal and wetland build. It is also used to simulate concentration field of wastewater discharged into Dian Lake which meets the discharge standard. The influences of wetland plants and water expanding on flow field and water quality are analyzed, and the effect of wastewater discharged into Dian Lake which meets the discharge standard on water quality is analyzed, too. The results show that: The influence of water expanding on flow field is local; and the influence of wetland plants on flow field occurs primarily at wetland areas; and the influence of water expanding on water quality is not great because the total phosphorus(TP) and the total nitrogen(TN) reduce to 1.69mg/L and 0.16mg/L from 2.08mg/L and 0.19mg/L respectively; and the influence of ecological wetland on water quality is great, because the TP and the TN reduce to 0.76mg/L and 0.05mg/L respectively, which could make the water quality of Dian Lake reach Ⅲ class of The National Surface Water Standards; and the influence of wastewater discharged into Dian Lake which meets the discharge standard on water quality is big, because the TP and the TN reduce to 0.17mg/L and 0.01mg/L respectively, which could obviously improve the water quality. Therefore, wastewater discharged into Dian Lake which meets the discharge standard and artificial wetland play an important role in the improvement of the ecological environment of Dian Lake.