Abstract: The electrochemical properties of AZ31B Mg alloy is investigated by electrochemical methods in MgSO₄-Mg(NO₃)₂ (0.14 mol/L MgSO₄, 1.86 mol/L Mg(NO₃)₂) electrolyte solution with different Na₂SnO₃ concentrations. The results suggest that AZ31B Mg alloy has the highest polarization resistance, the shortest delayed time and the lowest voltage drop when Na₂SnO₃ concentration is of 1 mmol/L. Moreover, the electrochemical impedance, galvanostatic discharge and linear polarization curves are used to research the effect of Mg electrode in the solution with and without Na₂SnO₃ at different immersion times. It indicates that Na₂SnO₃ can improve the corrosion resistance and discharge activity of Mg alloy at the same testing time. The surface structure and composition of Mg alloy is characterized by using scanning electron microscopy, and the results show that the improved electrochemical behavior of Mg alloy is related to the change of composition of corrosion products.