We studied acrolein (AC) adsorption on gold clusters Au (n) (n = 1-5) using density functional theory. It is demonstrated that conjugation effect reduces the adsorbate-substrate interaction through pi-(C=C), pi-(C=O) and di-sigma-(C=O) modes whereas it facilitates the di-sigma-(C=C) and the sigma-O configurations. Analysis reveals that in pi-(C=C) and pi-(C=O) modes acrolein uses the HOMO-1 orbital to interact with the clusters while in sigma-O mode the HOMO of AC plays the role. For di-sigma-(C=C), di-sigma-(C, O) and di-(C=O), the HOMO orbital of the cluster donates electrons to acrolein. Acrolein adsorption through the C=C bond is more favorable than that via the C=O group, which explains why the yields of C=C hydrogenation is higher than that of C=O reduction.