The regeneration process of fluid catalytic cracking (FCC) units produces amounts of greenhouse gases (GHGs), including carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ). However, the flue gas GHG emission characteristics of FCC units are not well understood in China. In our work, three typical FCC units are taken as stack tests for CO 2 , N 2 O, and CH 4 emissions in the flue gas. The on-site monitoring results show that the regenerated form of the FCC unit has the greatest impact on CH 4 , and CO 2 is the primary GHG, with total emissions of >99%. Meanwhile, the spent catalysts are collected for further characterization and regeneration experiments. Results show that the coke content and composition on the spent catalysts can directly affect GHG emissions. The regeneration experiments of spent catalysts at different oxygen contents show that the main emission temperature ranges of CO 2 , N 2 O, and CH 4 are 200−600 °C, 400−600 °C, and 300−600 °C, respectively. The peaks of CO 2 and N 2 O content in regenerated flue gas increase as the O 2 content increases, while CH 4 is generated under oxygenfree conditions. The study of the GHG emission characteristics can provide theoretical support for the carbon peaking and carbon neutrality goals.