Abstract: In respond to the problems of high free corrosion rate, anodic polarization, and potential hysteresis when AZ31 magnesium alloy is used as the negative electrode in magnesium batteries, suitable corrosion inhibitors and their dosage are sought to adjust the electrolyte to improve the discharge performance of the battery. The corrosion inhibition effect of the corrosion inhibitor Li₂CrO₄ was characterized by corrosion immersion test. Then the effect of Li₂CrO₄ dosage in Mg(ClO₄)₂ solution on the electrochemical properties of AZ31 magnesium alloy was studied by polarization curve and electrochemical impedance spectroscopy. Finally, the water-based magnesium-manganese battery was assembled for constant-current discharge as an application-side test. The results show that Li₂CrO₄ made the corrosion potential of AZ31 magnesium alloy shift positively with a maximum of 150 mV, and could improve the discharge platform of magnesium battery in the application of aqueous Mg-Mn battery. When the mass fraction of Li₂CrO₄ was 0.7%, discharge platform could be increased by about 0.15 V. When the mass fraction of Li₂CrO₄ was 1.2%, the corrosion of AZ31 magnesium alloy could be significantly improved in Mg(ClO₄)₂ solution, the discharge capacity of the aqueous magnesium manganese battery was up to 196.9 mA·h, which increased by more about 64% in comparison with blank solution, and the operating voltage was up to 1.39 V with a stable discharge curve.