Cities are the main carbon source among the terrestrial ecosystem types, and urban vegetation is an important carbon sink to mitigate carbon emissions from human activities in urban areas, but research on the influence of urban vegetation on urban atmospheric carbon dioxide is scarce, especially in developing countries. Most of the developing countries are in a subtropical climate zone, and the urbanization speed in developing countries is faster than that in developed countries. In order to promote the study of the carbon cycle in different ecosystem types, we studied the influence of vegetation on the CO₂ fluxes of the subtropical urban ecosystem in Fengxian University city, Shanghai, China. Using the 12-month flux observed and recorded by the eddy-related flux observation site in the study area and meteorological data combined with remote sensing data, the CO₂ flux dynamic characteristics and its influencing factors were analyzed. The main results are the following:(1) The study area was a carbon source, and the total annual CO₂ flux of the whole ecosystem was 9664.06 μmol m^-2 a^-1. The CO₂ flux growth rate reached a minimum of -4.48 μmol m^-2 d^-1 on May 6, 2017, with a CO₂ flux growth rate of 0 on July 30, 2017 and a maximum of 2.24 μmol m^-2 d^-1 on August 30, 2017. The CO₂ flux exchange in the growing season was lower than the CO₂ flux exchange in the non-growing season; these were 2169.58 μmol m^-2 月^-1 and 7494.48 μmol m^-2 月^-1 respectively; (2) Urban vegetation was a carbon sink, and its CO₂ fluxes decreased with the urban vegetation area in different wind sectors. The lowest mean value of CO₂ flux in the growing season appeared in the Northwest region and was 0.09 μmol m^-2 s^-1; (3) Leaf area index and plant biotic characteristics influence CO₂ flux. There was a negative correlation between CO₂ flux and leaf area index. Plant growth status and plant physiological activities affected the carbon cycling process of the subtropical urban ecosystem. This study can provide a reference for quantifying the effects of urban vegetation on atmospheric carbon dioxide and provide guidelines for the construction of green low-carbon cities in subtropical areas.