<p>In this paper, taking the four functional areas of Beijing in 2015–2021 as the research object, we calculated the carbon sink level and species diversity conservation level of urban ecosystem, respectively, and on this basis, the coordinated development of the carbon sink and species diversity conservation of urban ecosystem was measured. The results showed that: (1) The carbon sink level and species diversity conservation level of Beijing showed a significant upward trend from 2015 to 2021. Among them, the New Urban Development Area and the Ecological Conservation Area were higher than the Capital Functional Core Area and the Urban Functional Expansion Area. (2) The coordinated development of carbon sink and species diversity conservation of Beijing in 2015-2021 showed a relatively stable trend on the whole. From the perspective of different functional areas, the Ecological Conservation Area and the New Urban Development Area showed a good coordinated development, and most of them were in the state of “coordination” and “progress”, while the coordinated development of the Capital Functional Core Area and the Urban Functional Expansion Area were in the state of “uncoordinated” and “degradation”. (3) Further, according to the CI, it was found that the Capital Functional Core Area, the Urban Functional Expansion Area and the Ecological Conservation Area of Beijing belonged to the lagging type of carbon sink, while the New Urban Development Area transformed from the lagging type of species diversity conservation to the lagging type of carbon sink. The above results provide scientific support for optimizing urban ecological planning and formulating comprehensive strategies for low carbon and biodiversity conservation, crucial for advancing sustainable urban development.</p>