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Density functional theory calculations are presented for adsorption and dissociation of NH3,H2O,CH3OH,H2S and C2H4 on clean and oxygen atom pre-adsorbed metal surfaces (Cu,Ag,Au,Ni,Pd,Pt,Rh,Ru,Os and Ir).The calculation results indicated that the oxygen-promotion effect depends both on the metallic activity and the character of X-H bond.On the one hand,for a given reaction on a series metals,a good linear correlation was found between the energy barrier difference of X-H bond breaking on clean and oxygen-covered metals and the binging strength of oxygen on metals,namely oxygen-promotion effect was favorable to the less active metals but unfavorable to the more active metals.On the other hand,for a series X-H bond breaking reactions on a given metal,it was found that the promotion effect follows the trend of O-H>N-H>C-H,that is O-H bond is most promoted by the oxygen atom.The possible reason is the O-H bond forms the strongest hydrogen bond in transition state among the X-H bonds investigated in this work.Additional,it was found that the oxygen coverage has little effect on the X-H bond scission.