The structures and bonding properties of Al4Si2H2n (n = 0-10) clusters are systematically studied by using the evolutionary algorithm combined with ab initio computations. While the H atoms are bond on the terminal sites of the clusters at low H contents, the Al atoms are combined together by double H-bridges and the Al/Si atoms are tetrahedrally coordinated at high H contents. The Al4Si2H2n clusters break into a few fragments for n = 9,10. Analysis on the bonding natures shows that the Al-H bonds are strongly polarized and the Si atoms balance the charge states of the Al/H atoms according to the hydrogen concentrations. The hydrogen storage capacity in Al4Si2H16 cluster reaches 8.9 wt%, and the estimated strength of the hydrogen bonding is about -0.55 eV per H-2, which falls in the ideal window for reversible hydrogen storage at ambient temperatures. The high hydrogen capacity and moderate bonding strength suggest that Al-Si hydrides can be promising candidates for hydrogen storage. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.