Rare-earth based AB(5)-type alloys have wide application prospect in many areas such as gaseous hydrogen storage, hydrogen compressing, Ni/MH batteries etc. But opinions on their cycling degradation mechanism remain controversial, hindering them from further improvement. In this study, the hydrogen storage degradation mechanism of LaNi5-xAlx (x = 0, 0.25, 0.5) alloy system is studied using EXAFS as one of the main methods, and meanwhile the functioning mechanism of Al is illustrated. It is found that the hydrogen absorption/desorption plateau becomes tilted and the hydrogen storage capacity is decreased with cycling. These degradation phenomena are caused by the crystal damage due to the lattice strains as well as the mis-occupation of metal atoms during hydrogen absorption/desorption. Al with larger atomic radius stabilizes LaNi5 lattice structure by decreasing the lattice volume expansion rate upon hydrogenation and detaining the atomic migration during cycling, thus significantly improving the alloys' cycling stability from 89.1% (LaNi5) to 98.2% (LaNi4.5Al0.5) after 1000 cycles. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.