The effect of metal cations (Na+, Ca2+, Mn2+) on corrosion properties of Mg was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) 、weightloss measurement, and scanning electron microscopy (SEM/EDS) .The results show that the corrosion rate of Mg was affected by metal cations and the corrosion rate was in the descending order of Na+, Ca2+, Mn2+.This could be attributed to the incorporation of harder metal cations (Ca2+, Mn2+) into Mg during the immersion period, which could affect the structure of the films and form a more homogeneous and compact corrosion product film, thus slowing the corrosion dissolution process of Mg.The results of the experiment were in accordance with analytical resluts of Hard and Soft Acids and Bases (HSAB) principle.