Mass flux is an important basis for maintaining the relationship between lakes and rivers, while the key of mass flux is water flux. Aiming to a goal of constructing a clear water that are conducive to both the Yangtze River and Poyang Lake, the Poyang Lake Hydraulic Project (PLHP) in planning will be operated according to a proposed water level regulating scheme in the view of ecology, in which is controlling over the lake level in the dry season instead of the wet season. By using two-dimensional hydrodynamic model, this paper conducts a quantitative analysis concerning the potential impacts of the water level regulating scheme of PLHP under three typical hydro-years (wet, normal and dry years) on stream flow of the Yangtze River. According to the simulation results, during a PLHP water level regulating period, the difference, the discharge from the lake to the Yangtze River is very small, only varied from -0.2% to -0.7% compared with two modeling scenarios (with or without the PLHP). The discharge under those two scenarios is basically maintained in a balanced state, though the seasonal distribution time from the lake to the Yangtze River is changed. During the dry season, the project has minor impact on the flow of the Yangtze River, or even increases the amount of water discharges. The dry year has a maximum effect of the increased discharge, followed by normal year and the third by wet year. The increased discharge in different hydro-years varies from 2.1% to 17.0%. In normal year and dry year, the lake level before the beginning of the PLHP regulation is much lower than the highest regulated water level of 9 m, so that the existing PLHP regulation scheme, which proposes to regulate the water level to 14-15 m on September 15, has obvious defects and need a further optimization.