This work aims to control the degradation rate of biodegradable Mg by preparing corrosion inhibitor-loaded micro-arc oxidation/PLGA composite coating. The composite coating was prepared by means of micro-arc oxidation and dipping coating. Natural plant extract curcumin (Cur) was selected as the corrosion inhibitor. First, the MAO coating suitable for the composite corrosion inhibitor coating was prepared by the micro-arc oxidation technology, and then the PLGA-corrosion inhibitor coating was prepared on the micro-arc oxidation layer by the dipping coating to obtain the composite coating. SEM&EDS, AFM, and FTIR experiments were employed to analyze the microstructure and compositions of the coating. The corrosion resistance of the coating was evaluated through electrochemical tests and immersion tests in vitro. FTIR results showed that Cur was successfully loaded in the coating and did not react with PLGA. Electrochemical and immersion experiments in vitro showed the coatings effectively improve the corrosion resistance of magnesium alloy substrate. The results of potentiodynamic polarization tests turned out that the corrosion current density of MAO/PLGA-Cur coating was three orders of magnitude lower than that of the Mg substrate. The results of the immersion experiments in vitro indicated that the weight loss of the MAO/PLGA-Cur coating was reduced 62.04% and 26.63% when compared with the substrate and coating without Cur after 14 days of immersion respectively. The optimized parameter of micro-arc oxidation time was 10 min. The coating showed the best performance when the concentration of Cur was 0.12wt.%, the concentration of PLGA was 12wt.%, and the dipping coating process was 0 degrees.