The?degradation?property of biomedical magnesium alloy is the key to determine its application on cardiovascular stents and bone replacement material, etc. In this paper, we discussed the effect of degradation on magnesium alloy with various cations. AZ31B magnesium alloy samples were immersed into NaCl aq., KCl aq., MgCl2 aq. and CaCl2 aq. with the same concentration of Cl- used as body fluid. The potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) of these magnesium samples were analyzed. Results show that the corrosion potential and impedance have the similar tendency with the pH values and gravimetric curve. Namely, the metal cations affect the degradation property of magnesium alloy directly and the order is NaCl > KCl > CaCl2 > MgCl2. Na+ is superior to other cations in magnesium alloy degradation