Lithium-sulfur (Li-S) batteries are regarded as the promising next-generation energy storage device due to the high theoretical energy density and low cost. However, the practical application of Li-S batteries is still limited owing to the cycle stability of both the sulfur cathode and lithium anode. In particular, the instability in the bulk and at the surface of the lithium anode during cycling becomes a huge obstacle for the practical application of Li-S battery. Herein, a Li-rich lithium-magnesium (Li-Mg) alloy is investigated as an anode for Li-S batteries, based on the consideration of improving the stability in the bulk and at the surface of the lithium anode. Our experimental results reveal that the robust passivation layer is formed on the surface of the Li-Mg alloy anode, which is helpful to reduce side reactions, and enable the smooth surface morphology of anode during cycling. Meanwhile, the mixed electron and Li-ion conducting matrix of the Li-poor Li-Mg alloy as a porous skeleton structure can also be formed after delithiation, which can guarantee the structural integrity of the anode in the bulk during Li stripping/plating process. Therefore, the Li-rich Li-Mg alloy is demonstrated to be a very promising anode material for Li-S battery.