Base on underway surface CO2 data obtained from Changjiang (Yangtze River) Estuary and adjacent area in August 2019, combined with the temperature, salinity, dissolved oxygen and other parameters, the spatial variation of pCO2 and its controls during late summer were discussed briefly. The results show that the pCO2 generally decreases with distance offshore, and is the lowest in the mesohaline zone of river plume. After removing temperature effect, the good negative correlation between temperaturenormalized pCO2 and DO% indicates that biological processes are the main reason for the spatial variation, and the strong sink for atmospheric CO2 just results from high biological production. Moreover, the section distributions of temperature, salinity and DO% in the riverocean mixing zone show that the influence from vertical mixing on pCO2 is minor due to the water stratification. On the whole, the airsea CO2 fluxes for the study area are -2.0±5.2 mmol·m-2·d-1, showing a carbon sink with respect to atmospheric CO2. However, with environment changes and human perturbation such as the decrease of Changjiang runoff, Changjiang Estuary and its adjacent area may gradually shift from a sink to a source, which is necessary for us to pay more attention and further study.