Magnesium alloys are widely used in aerospace, automobile and electronic products because of their low density and high specific strength. However, the poor corrosion resistance of magnesium alloys limits their application. To improve the corrosion resistance of magnesium alloys, Bi and Gd were used for alloying, and a Mg-1Bi-0.5Gd (0.94 wt. %Bi, 0.53 wt. %Gd) alloy was prepared via a reverse extrusion process. The microstructure and corrosion behavior of the Mg-1Bi-0.5Gd alloy before and after extrusion were studied via XRD, OM, SEM, hydrogen evolution experiments and electrochemical tests. The results show that, compared with the homogeneous alloy, the extruded Mg-1Bi-0.5Gd alloy has greater corrosion potential and a lower corrosion current density, resulting in better corrosion resistance, which is attributed to the extrusion process further refining the grain structure of the alloy and significantly improving its corrosion resistance. Key words： reverse extrusion; Mg-1Bi-0.5Gd alloy; electrochemistry; grain refinement.