Abstract: In order to understand the carbon exchange patterns and carbon cycling mechanisms of farmland ecosystems, this study used eddy covariance method to observe the fluxes of rice-oilseed rape double cropping farmland ecosystems in central Hunan Province throughout the year, and analyzed the changes of carbon fluxes and their components at different time scales, and explored the responses of carbon fluxes to major environmental factors during the growing seasons of rice and oilseed rape. The results showed that the daily variation of net carbon exchange in rice-oilseed rape double cropping farmland ecosystems showed a "U"type single-peak curve, and the seasonal variation showed a single-peak double-valley "W"curve, and there were two obvious carbon uptake periods. The peak of NEE uptake was generally higher in rice than in rape and the accumulation rate of GPP and R_eco was higher in rice than in oilseed rape; the total accumulation of net carbon exchange was -206.26 g/m², the total accumulation of total primary productivity was 1 173.9 g/m², the total accumulation of ecosystem respiration was 967.64 g/m², and the carbon use efficiency of the ecosystem was 17.6%, which generally showed that carbon uptake was strong. The correlation between carbon fluxes and environmental factors was different between rice and oilseed rape during the growing season, and the net carbon exchange during daytime was negatively correlated with photosynthetic effective radiation. The results of this study can provide theoretical basis and data support for carbon sequestration and emission reduction in farmland.