Flow regime change is the main dynamics to affect the lake ecological system evolution. It is worth studying that how the proposed Lake Poyang hydraulic project (PLPHP) will impact the hydrology and hydrodynamics of Lake Poyang. Based on the EFDC model, a two-dimensional model of Lake Poyang hydrodynamics is constructed. According to the planning water level regulation scheme of PLPHP, this research discusses the possible influence of PLPHP on hydrology and hydrodynamics of Lake Poyang using the method of scenario simulation (including normal, dry and wet hydro-years). The simulation result shows that the 11m controlled water level in eco-adjustment period of low-water level (from Dec. 1st to the end of Mar. or early Apr.) will effectively uplift the average water level of Lake Poyang in this period. The maximum uplift of average water level in the lake will be 2.59 m in wet hydro-year (2010), 4.35 m in dry hydro-year (2004), 2.68 m in normal hydro-year (2000),respectively. These uplifts of water level in eco-adjustment period of low-water level will lead to the different level decreases of average flow velocity, maximum flow velocity and minimum flow velocity of low-water level period in different hydro-year scenario. The maximum decrease of flow velocity is in the waterway of Lake Poyang into the Yangtze River (which is located in Xingzi to Hukou), in which drop in average velocity is more than 44% in 2000 and 2010, 50% in 2004, but the effect of flow velocity on two natural reserves is small. As to the effect of flow pattern, the main result shows that because of the 11 m controlled water level with PLPHP scenario, the flow pattern is apparently different from that without PLPHP in the north of Tangyin, especially in the waterway of Lake Poyang into the Yangtze River. Furthermore, the region, in the vicinity of Tangyin and south of Songmenshan, will show larger water surface with more complex flow pattern when the volumes of flow in middle and south two branches of Ganjiang River are larger. Because of the uplift of water level and the drop of flow velocity, PLPHP has significant impact on water exchange cycle (WEC) of lake and WECs in different hydro-year scenarios are affected to varying degrees, the average WEC increasing by 5.6 d in 2004, the extent of impact being 26.1%. Therefore, the simulation results can reveal the impact extent of PLPHP on hydrology and hydrodynamics with the planning water-level regulation scheme, and provide some foundation at support to study the influence of PLPHP on water quality and ecological system evolution.