The dynamic and kinetic evolution of supported metal particles in the presence of reactants is deci- sive in shaping the nature of the catalytic active sites and the deactivation process. Ostwald ripening of FeO/Pt(111) supported Au particles in the presence of carbon monoxide is addressed here by first- principles kinetics. It is found that CO stabilizes the ripening monomer (Au atom) by forming favorable Au carbonyls with lower total activation energy, and corresponding phase diagram at wide range of tem- perature and CO pressures is constructed. Evolution of particle number, dispersion and particle size dis- tribution of supported Au particles are explored. Great influence of CO promotion on ripening kinetics is revealed and explored in details, and mbar range of CO can lower the onset temperature of ripening by a few hundred kelvins. The present work reveals the crucial role of the metal-reactant complexes formed under reaction conditions on ripening of metal catalysts.