A novel AS61 magnesium alloy is prepared via the small-hole confinement of liquid alloy by using a thick-walled copper mould. This facile method gives rise to distinct grain refinement and dispersed second phases such as nano-scale Mg2Sn (12.54 ± 3.35 nm). Benefiting from the unique microstructure, the AS61 shows enhanced anode performance when adopted for primary aqueous battery, as compared with that using the anode of the same composition fabricated via a common iron mould during melting and casting. The Mg-air battery with the novel AS61 anode provides a high voltage of 1.269 V at 10 mA cm-2; its anodic efficiency at 10 mA cm-2 reaches 78.4%, which is higher than lots of other types of magnesium anodes. Moreover, the discharge mechanism of AS61 is also unravelled based on electrochemical response and microstructure characterization.