Abstract: The main active particles produced by excitation of dielectric barrier discharge plasma on air were analyzed with emission spectrometry, the evolution rules of the active particles were simulated with plasma kinetic model, and the chemical kinetics mechanism of O-atom assisted ignition was revealed via sensitivity analysis and reaction path analysis. The results show that the main excited particles of N2 and O2 are generated with excitation of plasma on air, and the excited particles increase with the increase of voltage which will be to rapidly convert into free radicals and O-atom is the largest concentration of free radicals, and that the ignition delay time decreases about an order of magnitude, the oxidized pathway of CH3 changes to HO2 and O-atom from O2 for auto-ignition, and the latter reaction rate is much faster, that is why O-atom decreases the ignition delay time.