The influences of magnesium addition on the discharge performance and hydrogen evolution reaction behavior were studied via measuring discharge current, discharge potential, polarization curve and hydrogen evolution rate of lithium anodes in alkali aqueous solution. The results show that the hydrogen evolution rate is decreased by adding 0.07wt%Mg to lithium anodes. It is found that the current efficiency of lithium-magnesium alloy anodes is higher than that of lithium anodes, and the discharge current density of lithium-magnesium alloy anodes is a little lower than that of lithium anodes. The discharge potential of lithium-magnesium alloy anodes is a little more positive than that of lithium anodes when the discharge current density is high. The polarization curves show that the open circuit potential of Li-0.07wt%Mg anodes is a little more positive than that of lithium anodes. The micro-cell corrosion current density of Li-0.07wt%Mg anodes is near to that of lithium anodes. The analysis of X-ray diffraction shows that after discharge the surface film of the lithium-magnesium alloy anodes mainly consists of LiOH, LiOH·H2O and some Mg(OH)2. Scanning electron microscopy images show that the surface film of lithium-magnesium alloy anodes is less porous than that of lithium anodes after discharge, namely, the decrease of hydrogen evolution rate by magnesium addition is related to the integrity of the surface film enhanced by Mg(OH)2