Abstract: The ocean is an important source of carbon monoxide (CO) in the atmosphere, and estuarine regions play an important role in regulating the balance of climate-active gases. This study aims to investigate the status of the Changjiang Estuary as a typical estuary in the global marine CO biogeochemical cycle, as well as to further understand the variations in CO concentrations in estuarine seawater and the atmosphere. Field surveys were conducted in the winter and summer of 2021 in the Changjiang Estuary and its adjacent waters to study the distribution of CO, sea-to-air fluxes, and microbial consumption rate of CO. The results showed that the average volume fractions of CO in the surveyed waters in winter and summer were (530.39 ± 120.40) × 10⁻⁹ and (416.91 ± 102.01) × 10⁻⁹, and the atmospheric CO content was greatly influenced by human activities. The mean concentration of CO in summer (4.52 ± 2.13) nmol/L was significantly higher than that in winter (1.30 ± 0.79) nmol/L due to the influence of light intensity and input of organic matter from land sources. Correspondingly, the mean sea-air flux in summer 0.95 μmol/(m²·d) was significantly higher than that in winter 0.10 μmol/(m²·d). In the study of microbial consumption rates, the average values of the microbial consumption rate constant (k_bio) in winter (0.46 ± 0.31)/h was significantly higher than that in summer and (0.26 ± 0.07)/h, and the distribution of k_bio did not show significant spatial variation in the study area. The data provided in this study can help us deepen our understanding of the status of estuarine regions in the global marine CO biogeochemical cycle.