Poyang Lake is a typical representative of the floodplain lakes and wetlands in the middle reaches of the Yangtze River. The high-amplitude water level fluctuations undoubtedly alter the heat flux processes, profoundly affecting the surface ecological hydrological processes and local climate characteristics. To study the response mechanisms of Poyang Lake"s heat flux to the flooding process, this paper quantitatively simulates the hydrological and energy processes of the Poyang Lake floodplain wetland by using the improved VIC land surface model and its Lake module. It investigates the seasonal variation characteristics of the water-heat flux in the wetland and analyzes the driving mechanisms of the flooding process on the spatial-temporal distribution of heat flux. The results show that: (1) The model demonstrated robust performance in simulating flood dynamics and heat fluxes in Poyang Lake. For hydrological simulation, the monthly averaged water level simulations showed high consistency with observed values, achieving superior correlation coefficients (R > 0.9) and Nash-Sutcliffe Efficiency coefficients (NSE > 0.8). In thermal flux modeling, the simulated Bowen ratio exhibited strong agreement with reference values, yielding a correlation coefficient of 0.81 and NSE exceeding 0.7. This modeling framework reliably captures the hydrological rhythms and spatial heterogeneity of flood inundation in Poyang Lake, providing an effective tool for investigating eco-hydrological processes in lake wetlands under climate change scenarios; (2) In terms of temporal process, Seasonal dynamics of energy partitioning are significantly modulated by flood inundation processes in Poyang Lake. During the high-water period, extensive inundation shifts the energy allocation toward a "high latent heat–low sensible heat" state under water-dominated surfaces: 68% of net radiation is allocated to latent heat flux, driving Bowen ratio down to 0.09 (vs. 0.38 in non-inundated periods). Following emergent mudflat exposure in the dry season, latent heat contribution declines to 56%;(3) in the spatial pattern, Energy partitioning exhibits marked contrasts between the lake area and surrounding terrestrial regions: Lake-dominated zones show 29% higher latent heat flux and 59% lower sensible heat flux compared to peripheries. The northeastern high-frequency inundation area forms a persistent latent heat flux hotspot (annual mean: 89 W·m?2), exceeding levels in the southwestern low-frequency inundation zone by 80%. Spatially, latent heat flux exhibits a distinct "northeast-high to southwest-low" gradient;(4) The energy partitioning exhibits a three-stage relationship with soil moisture/water level: When the volumetric water content of the wetland surface soil is below 17%, the evaporative fraction increases relatively slowly with rising moisture content. Once the soil moisture exceeds 17%, the evaporative fraction shows a linear positive correlation with moisture content. When the soil moisture surpasses 32%, the evaporative fraction becomes decoupled from soil moisture under inundation conditions and is no longer constrained by soil moisture, demonstrating that soil moisture exerts distinct phased regulatory effects on the evaporative fraction. This study couples the land surface model VIC with underwater terrain inundation analysis to reveal the regulatory mechanism of Poyang Lake"s floodplain processes on regional energy balance. It provides a new method for understanding the water-heat exchange mechanisms in floodplain wetlands, offering important scientific insights into the ecohydrological processes of floodplain wetlands under climate change.