The paper aims to obtain magnesium alloy anodized film of good corrosion resistance through the anodizing process of stearic acid additive. Anodization was carried out in alkaline oxidizing solution containing 2 g/L of stearic acid by the DC power anodization method. The microstructure and the thickness of the oxide film were analyzed with SEM, ImageJ software and TT230 thickness gauge; the film composition was analyzed by FTIR, XPS and XRD; the corrosion resistance of the film was detected by electrochemical test. The results showed that the porosity, pore size and number of pores of the oxide film prepared by this method were reduced, while the thickness and the density of the film layer were increased. The self- corrosion current density of the film layer was reduced to 3.15×10–7 A/cm2, which was decreased by two magnitudes compared with the oxide film without stearic acid additive. The corrosion resistance of the film layer was improved significantly. The stearic acid additives can improve the corrosion resistance of the film by increasing the film formation voltage, enhancing the spark discharge effect, surfactant action and changing the composition of the film.