Modification surface treatment of ZM5 Mg alloy by high-energy micro-arc spark alloying S331 was conducted to improve the corrosion resistantance of the alloy. The results reveal that the hardness of the alloying layer is improved from HV85 of the ZM5 substrate to HV250. The microstructure of the alloying layer was observed by OM （optical microscope） and SEM （scanning electron microscope）

and composition distribution in the alloying layer was determined by EPMA. Meanwhile

the corrosion behavior of the alloying layer was analyzed by the potentiodynamic polarization curve. The results show that the microstructure of alloying layer is refined

and Al and Mn element concentration is higher than that in the substrate. Self-corrosion potential and corrosion current density in the alloying layer are significantly decreased

which are responsible for the improvement of the corrosion resistance.