Abstract: As an important measure of green stormwater infrastructure, bioretention facilities also emit greenhouse gases (GHGs) such as carbon dioxide (CO₂) and Nitrous oxide (N₂O) in removing pollutants from stormwater runoff. At the same time, plants have the function of carbon sequestration through photosynthesis. However, there is a knowledge gap on the GHG emission characteristics of bioretention facilities and how they are affected by the carbon-to-nitrogen ratio (C/N). Using the laboratory column experiment, artificial rainwater was configured to simulate the runoff volume and water quality of urban road stormwater runoff. The influence of C/N ratio in stormwater runoff on GHG emission characteristics of bioretention facilities was systematically investigated, and the control effects on water quantity and water quality were analyzed. The results showed that C/N had a significant impact on GHG emissions and global warming potential (GWP). Among them, C/N had a greater impact on N₂O emissions. When C/N=15, the average emission flux of N₂O was the largest, which was 166.32 μg/(m²·h). When C/N<1, the average emission flux of N₂O was the smallest, which was 31.26 μg/(m²·h). GWP increased with the increase of C/N. When C/N=15, GWP value was approximately four times that of C/N<1. Moreover, when C/N<1, the bioretention facilities had the greatest carbon reduction capacity and showed the best control effect on the water quality and quantity in stormwater runoff. This study can provide support for the assessment of carbon emission reduction potential of bioretention facilities.