Abstract: CO₂ flux and impact factors were measured by eddy correlation system in winter wheat fields. The results show distinct diurnal and seasonal variations in CO₂ flux in winter wheat fields with an inverted U-shaped diurnal change in CO₂ flux for every growth stage. CO₂ instantaneous peak and cumulative fluxes are maximum at headgrouting stage, next highest at heading stage and lowest at re-greening stage. Latent heat flux, sensible heat flux, net radiation flux and photosynthetic active radiation are all significantly positively related with CO₂ flux. The correlation coefficient of latent heat flux to CO₂ flux is 0.920～ 0.955, which is higher in seedling, jointing and heading stages, and lower in filling stage. That of sensitive heat flux to CO₂ flux is 0.801 ～ 0.953, higher at jointing stage, next at seeding stage but low at heading and filling stages.That of net radiation flux to CO₂ flux is 0.879 ～ 0.967, higher at seeding, jointing and heading stages, but lower at filling stage. That of photosynthetic active radiation to CO₂ flux is 0.910 ～ 0.953,lower at prophase and anaphase than at metaphase. The results also indicate that irrigation improves CO₂ flux to a certain extent.