The Mg17Al12 intermetallic compound is brittle and easily pulverized and hydrogenated, which holds the promise as a hydrogen source because the theoretical hydrogen generation capacity by hydrolysis of Mg17Al12 hydride (MHA) is as high as 13.6 wt.%. However, it was found that the hydrolysis reaction of MHA without any additives would be rapidly interrupted because of the formation of a passive layer on the surface of the particles. The influence of CaH2 on the hydrogen generation performances of the MHA + CaH2 mixtures by hydrolysis was investigated in this paper. The result showed that the addition of CaH2 by ball-milling is effective to improve the hydrolysis reactivity of the mixtures. The best was obtained by MHA+10wt.% CaH2 mixture ball-milled for 1 h, which produces 1389 ml H-2/g at 70 degrees C after 1 h of hydrolysis in pure water, namely the hydrogen generation yield reaches 94.8%. In this paper, the reasons of the improvement and the reaction mechanism have also been discussed respectively. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.