Groundwater dynamics and variabilities of floodplains play an important role in affecting river and lake water resources, water pollution and eco-environment functions, due to the change of its hydrological regimes. The floodplain wetlands of Lake Poyang are located strategically in the middle and lower reaches of the Changjiang River, while its dynamic behaviors of water resources and water exchanges have many uncertainties. This study focuses on the typical floodplain area of Lake Poyang. We used a two-dimensional groundwater flow model to simulate floodplain surface water-groundwater interactions and the associated exchange fluxes. The results show that floodplain groundwater recharges to lake during the dry and recession periods, while lake recharges to groundwater during the rising and flooding periods. Groundwater levels across the whole floodplain exhibit a similar variation trend to lake water levels. Variation amplitudes of groundwater levels adjacent to the main lake are distinctly higher than those of the floodplain. In general, groundwater flow velocities in the northern area are obviously higher than those in the southern area, and the main lake regions are higher than the lake's floodplain, with velocity values less than about 1-2 m/d. Water budget analysis indicates that floodplain groundwater system mainly receives rainfall (52%) and lake inputs (39%), and losses water by groundwater evaporation (72%) and discharging to lake (24%). Additionally, recharge process of the groundwater system mainly occurs during the spring and summer seasons, and discharge process occurs during the autumn and winter seasons. In conclusion, surface topographical features play a dominant role in controlling groundwater level distributions and flow fields, but the dynamics of lake water levels are regarded as a key force that leads to a seasonal variation of the lake-groundwater exchange. The outcomes of this study can provide scientific references for future water resources management, allocation, and sustainable development of the eco-environment ofthe Lake Poyang floodplain wetlands.