Abstract: The influence of H₂/CO doping on soot formation in laminar ethylene diffusion flame in O₂/CO₂ atmosphere was studied by extinction experiment and CoFlame program simulation.The distributions of flame height, temperature, content of soot and important components were obtained, and the variation of main soot evolution process was analyzed. The results show that the addition of H₂/CO has obvious inhibition effect on soot formation in ethylene flame. When the flow ratio of H₂ to CO is 0.3∶0.3, the inhibition effect is the strongest, and the soot volume fraction decreases by 25.3%. The effect of H₂/CO doping on the height and temperature of ethylene flame is weak, the thermal effect and oxidation rate are not the main factors affecting soot formation in ethylene flame. It is mainly through inhibiting the formation of acetylene, benzene and pyrene, then inhibiting the soot nucleation and soot surface growth, and finally reducing the soot formation.