Abstract: Moderate or intense low-oxygen dilution （MILD） combustion is an advanced low-oxygen diluted combustion technology capable of achieving simultaneous reductions in NO_x and soot emissions. This study employs numerical simulations based on the counter-flow flame model in the chemical kinetics analysis software CHEMKIN-PRO to investigate the soot formation pathways in propane MILD combustion and their distinctions from conventional combustion. Furthermore, the effects of strain rate （50–80 s⁻¹） and CO₂ dilution （volume fraction: 0–60%） on soot formation pathways under MILD conditions are systematically analyzed. The results reveal that the dominant soot formation pathways in MILD combustion are: 2C₃H₃→A1, A1⁻+H（+M）⇌A1（+M）, A1⁻+CH₄⇌A1+CH₃, A1⁻+C₂H₄⇌A1+C₂H₃, C₆H₅CH₃+H=A1+CH₃ and C₄H₅⁻²+C₂H₂=A1+H; Compared to conventional combustion, the reaction rates of 2C₃H₃→A1 and A1⁻ + H（+M）⇌ A1（+M） under MILD conditions are significantly reduced, leading to suppressed A1 formation and thus inhibiting soot nucleation. Consequently, the surface mass growth rate of soot decreases by 78.6%, and the peak soot volume fraction diminishes by 83.7%. Notably, the contribution of the 2C₃H₃→A1 pathway to soot formation decreases by 7.7% under MILD combustion, while the importance of the C₆H₅CH₃+H⇌A1+CH₃ and C₄H₅⁻² + C₂H₂⇌A1+H pathways increases by 5.36% and 7.59%, respectively. Additionally, the peak soot volume fraction under MILD conditions exhibits a nonlinear dependence on strain rate, initially increasing and subsequently decreasing with rising strain rates. This behavior stems from the competitive interplay between the non-monotonic variation in nucleation rates and the continuous increase in surface growth rates. Both the physical and chemical effects of CO₂ dilution intensify with higher dilution ratios. At CO₂ dilution levels of 0−40%, the physical effect of CO₂ exerts minimal influence on peak soot volume fraction. However, CO₂ chemically promotes H consumption via the CO+OH⇌CO₂+H reaction, thereby weakening the H-abstraction-C₂H₂-addition （HACA） mechanism critical for polycyclic aromatic hydrocarbon （PAH） growth. This results in significant reductions in A1 and A4 concentrations. At 60% CO₂ dilution, the peak soot volume fraction further declines to 6.4×10⁻⁹, demonstrating enhanced suppression of soot formation in MILD combustion.