In this study, we used the Carnegie-Ames-Stanford Approach (CASA) model, carbon and industrial oxygen production methods to calculate the carbon sequestration oxygen release amount and its value in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in 2015, and combined with European Space Agency (ESA) Climate Change Initiative Land Cover (CCI-LC) products, we discussed the evolution of the terrestrial ecosystem in the study area from 2000 to 2015 and the changes in carbon sequestration oxygen release and its value. The findings suggest the following: (1) During 2000-2015, the urban expansion of the study area was obvious, mainly manifested as the encroachment of urban land on farmland and grassland. (2) 91.03% of the total amount and value of carbon fixation and oxygen release were provided by the forest and farmland in the GBA. The terrestrial ecosystem changes in the GBA during 2000-2015 had brought about losses of 53.49 G g in carbon fixation and 518.65 G g in oxygen release, respectively, and the corresponding values decreased by 179 million yuan and 206 million yuan, respectively, of which 91.75% of these losses were caused by urban encroachment on other land use types. (3) The carbon fixation and oxygen release values have a strong negative correlation with urban coverage, which means that urban expansion can significantly reduce the carbon fixation and oxygen release values. On the contrary, there is a strong positive correlation between the value of carbon fixation and oxygen release and the forest coverage, and the increase in forest coverage is beneficial to the increases in the carbon fixation and oxygen release values. In this paper, the "neighborhood proxy method" was used to obtain the variations in the amount of carbon fixation and oxygen release and the values thereof caused by the terrestrial ecosystem changes, which was worth of widely use. Looking ahead, the government of the GBA is highly recommended to optimize the structure of terrestrial ecosystems by controlling urban expansion, protecting forest resources and reducing the artificial role but enhancing the natural role in the ecosystem changes, so as to achieve green sustainable development.