Afforestation projects were applied in the Poyang Lake Basin of China at the beginning of 1980s. The large-scale plantation may dramatically influence the changes in carbon storage of forests in this basin. Therefore, climate-induced variations in the carbon balance of the Poyang Lake Basin's forests may play an important role in the carbon cycle of China. However, we have little understanding of their long-term behavior, especially the future trend of carbon sink/source patterns under climate change and rising atmospheric CO₂. The annual carbon budget of the Poyang Lake Basin's forests during 1981–2050 was estimated by using the Integrated Terrestrial Ecosystem Carbon-budget model (InTEC) coupled with projected climate change simulated by Regional Integrated Environmental Model System (RIEMS 2.0). During 1981–2000, the rapid increment of annual NPP in this basin was possible due to large plantation. Soil organic carbon storage (0–30cm) of forests generally decreased by 1.0% per year at the beginning of plantation. Moreover, forests in this basin converted from carbon source in 1980s to carbon sink in 1990s. By 2040–2050, total carbon stocks of forest ecosystems will increase by 0.78Pg C, compared to recent years (2001–2010). Under future climate and CO₂ concentration in A1B scenario, NEP of forests in Poyang Lake Basin lean to keep relative stable (20-30Tg C y^-1) because of old forests except for some years induced by extreme droughts. Our results also showed that prediction of NEP of forests in Poyang Lake Basin was controlled by water limitation; in contrast, temperature was the main factor on inter-annual variability of NPP.