The mechanism of the improvement of the cycling stability of the La-Mg-Ni-Co based hydrogen storage alloy electrode was systematically investigated. The results show that the cell volume expansion upon hydrogenation is obviously decreased after the partial substitution of Al for Ni. Therefore a decrease in the pulverization of the alloy particles is obtained,which leads to the decrease of the contact area of the fresh alloy surface with alkaline electrolyte and the increase of the charge/discharge efficiency. Moreover,the occurrence of Al in the alloy can create a dense Al oxide film on the surface of the alloy during charge/discharge cycling. This dense oxide film can prevent further oxidation of the active components in the alloy,which is believed to be the most important factor responsible for the improvement of the cycling stability of the La-Mg-Ni-Mn-Co-Al type alloy electrodes.