Abstract: Estuarine wetlands have unique biochemical characteristics different from other ecosystems. The net ecosystem exchange (NEE) of carbon dioxide was studied preliminarily by open-path eddy covariance at the Chongxi Wetland, Yangtze Estuary. The results showed that during the growing season, the NEE of carbon dioxide showed a distinct V-like diel course, with a mean emission rate of -0.06 mg/(m2>/sup>·s). The NEE lacked a diurnal pattern, and it fluctuated above zero with an average emission rate of 0.025 mg/(m2>/sup>·s) during the non-growing season. It conformed to carbon exchange characteristics of other ecosystems mainly due to plant photosynthesis and carbon fixation in the growing season. The NEE in the non-growing season was more largely affected by soil temperature than that in the growing season. Carbon dioxide emissions from ecosystem to atmosphere during neap tides were higher than those during spring tides in both the growing and non-growing seasons, which indicated an inverse correlation between carbon dioxide emissions and tidal height, and that high water level inhibited ecosystem respiration and the transport of carbon dioxide and therefore further reduced carbon dioxide emission. The net photosynthetic rate of plants during the neap tides was similar with that during the spring tides, suggesting that the tide had little influence on plant photosynthesis and carbon fixation at the same site. The tide affected the net ecosystem exchange of carbon dioxide mainly by reducing carbon dioxide emissions from soil respiration. In summation, the Chongxi Wetland is a carbon sink in whole year period.