The water level and flow velocity are the key factors in maintaining and improving the ecological environment of the artificial lakes. In order to study and analyze the influences of the water level upon the flow velocity distribution, the numerical simulations of the flow field of the Yanming Lake are carried out based on a two-dimensional hydrodynamic model. And the simulations include the influences of a single-factor water level on the flow velocities and the influences of the measured level of exchanged water on the temporal and spatial distribution of the flow velocities during water level fluctuation. The simulated results indicate that the water level is one of the factors influencing hydrodynamics, and the flow velocity in the Yanming Lake is greater than that during high water level and distribution. In addition, as the water level falls and rises, there is a little influence on the circulation. During the water exchange, there is no obvious difference in the water level distribution in the high water level periods; the water depth increases progressively from the upstream to the downstream. In the low water level periods, the water level distribution is different, the flood plain is exposed, and the water depth distribution varies greatly. When the water level changes, the water level from the upstream to the downstream of the Yanming Lake shows a gradient change, and the water depth varies with the water level; and the spatial and temporal distribution of the flow velocities verifies the impacts of the single-factor water level on the flow velocities, and it is also shown that the different water levels have different effects on the flow velocities and the flow velocity distribution. The numerical simulation analysis results show that the water level of the artificial lakes can improve their hydrodynamics, and can provide scientific references for their regime management.