In this paper, the mechanisms of H-2 evolution on Pt-6, Pt5Sn5, and Pt3Sn6 clusters were respectively investigated by the B3LYP method of density functional theory (DFT). The B3LYP functional with non-local dispersion corrections (B3LYP-D3) method were performed to investigate the adsorption of H and H+ on clusters. The calculation results indicated that the adsorption energy of H on Pt reduced due to the interaction of Sn and Pt, which promoted H desorption from Pt to form H-2. Meanwhile, Sn atom of Pt5Sn5 and Pt3Sn6 clusters had strong interaction with H+ due to the existence of Pt, which was benefit for the reduction of H+ on Sn atom. As a consequence, Pt5Sn5 and Pt3Sn6 showed lower potential barrier and higher activities than Pt for H2 evolution. The potential barriers of H-2 formation over Pt3Sn6 clusters was only 11.1% of that over Pt cluster. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.