On the basis of Langmuir-Hinshelwood mechanism, with density functional theory method, all the dehydrogenation reactions in both Samanos mechanism and Moiseev mechanism in acetoxylation of ethylene to vinyl acetate, i.e., the dehydrogenation of ethylene, acetic acid and hydrogenated vinyl acetate (VAH), on Pd/Au(100) surface consisting of two diagonal Pd atoms were taken into consideration to examine the influence of surface oxygen atoms and hydroxyl groups on these dehydrogenation reactions. Besides, the corresponding adsorption of relevant species was investigated and the energetics of the dehydrogenation reactions was compared. Our calculations show that the surface Os kinetically facilitate ethylene dehydrogenation, but surface OHs kinetically inhibit ethylene dehydrogenation; the surface Os and OHs can kinetically facilitate acetic acid dehydrogenation, while they are kinetically unpreferable for VAH dehydrogenation; both surface Os and OHs are thermodynamically favored for the dehydrogenation of ethylene, acetic acid and VAH. [GRAPHICS] .