The present study demonstrated the novel control on nanostructures and reactivity of soot by CO2 local micro-injection in ethylene inverse diffusion flames. Both global and local sampling methods were employed to capture soot particles at different flame positions. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were applied to investigate detailed soot characteristics. The results indicated that, when CO2 was added using micro-injection in flames at micro flow rates, the soot exhibited turbostratic structures with amorphous characters and had shorter fringe length and larger fringe tortuosity related with higher oxidation reactivity compared to soot from the pure ethylene flame, which inferred that CO2 addition could be beneficial to enhance soot oxidation and make the soot to have a low carbonization. Especially, the injection of CO2 in flames caused an obvious effect on delaying and decreasing in soot nucleation and growth rates during soot evolution process. The properties of soot from the global quartz plate sampling were quite similar for different local injection positions. However, it was worth noting that the direct addition of CO2 through the oxidizer pipe at same flow rates had no significant effects on soot characteristics. (C) 2019 Elsevier Ltd. All rights reserved.