The density functional theory (DFT) was applied to investigate the adsorption and growth of Pt-n (n = 1-4) clusters and hydrogen spillover on gamma-Al2O3 surface, which is of importance for many catalysis reactions. It was found that the growth ability of the supported Pt-n cluster is weaker than the gas phase Pt-n clusters. Basin structures on both of the clean and hydrated surfaces were found to stabilize the Pt clusters. For the hydrated surface, the basin structure, together with the size of Pt-n cluster, was also found to take trivial impacts on the hydrogen spillover. The most feasible supplier of H species on the hydrated gamma-Al2O3 surface was identified. Additionally, it was interesting to found that there would be an optimized size of the supported Pt-n cluster at n > 3. (C) 2014 Elsevier B.V. All rights reserved.