Rare-earth Mg-based hydrogen storage electrode alloys of LaMg2Ni9-xCox(x=0.3~6.0) and MlMg2Ni9-xCox(x=0.3~4.5) with different stoichiometric ratios were prepared by coprecipitation-reduction-diffusion method. Electrochemical analyses showed that the alloys prepared by this method can be easily activated; with x increasing, no obvious change for the activity numbers, and the discharge capacity decreased and the cyclic stability of alloy electrodes was effectively improved. Their activity numbers were larger than La-alloys, the discharge capacity decreased and the cyclic stability of mix-alloys was better than La-alloys. Structure analyses showed that the main phases of alloys were MgNi2 and LaNi5, the amount of LaCo5 phase and LaCo3 phase increased with Co content increasing.