The purpose of this study is to investigate the characteristics of soot particles in C2H4/CO2/O-2/N-2 combustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO2/O-2/N-2 mixture, the key species C2H2, C3H3 responsible for formation of first aromatic ring, the typical aromatics and 4-ring aromatics total production rate all decrease greatly. In addition, with CO2 mole fraction from 0.2 to 0.5 in the mixture, the soot particle number density, volume fraction, surface area density, which are three most important parameters to soot particle property, are suppressed obviously. Furthermore, the increasing content of CO2 in the oxidizer influences mostly H, OH radical concentrations by two reactions: CO + OH=CO2 + H and H + O-2=O + OH, and the production rate of H, OH from the two reactions declined, which revealed that CO2 in mixture has an inhibiting effect on soot particle generation.