In order to study the effects of the surface microstructure of micro arc oxidation (MAO) coating on the structure and properties of MAO/ diamond ⁃like carbon (DLC) film composite coating, MAO coatings with different roughnesses were prepared on the surface of magnesi⁃ um alloy by voltage regulation, and then MAO/ DLC composite coatings were constructed by unbalanced magnetron sputtering. The microstructure, roughness, thickness, mechanical properties, friction and wear properties and corrosion resistance of the coatings were studied by scanning electron microscope (SEM), electron energy dispersive spectroscopy (EDS), surface roughness tester, scratch tester, friction and wear tester and electrochemical workstation. Results showed that when the roughness of MAO coating increased gradually from 0.19 μm to 0.57μｍ, the surface porosity of MAO coating increased from 9.429% to 12.924%, the friction coefficient increased from 0.53 to 0.66, and the self⁃corrosion potential shifted negatively from -1.571 V to -1.595 V. Moreover, the roughness of 3.1 μm thick DLC film deposited on the surface increased from 0.22 μm to 0.58 μm. The surface porosity increased from 1.553% to 6.074%, the friction coefficient increased from 0.24 to 0.45, the wear rate increased from 2.01×10^-5 mm³/(N·m) to 8.41×10^-5 mm³/(N·m), and the self ⁃ corrosion potential shifted positively from -1.547 V to -1.486 V. Meanwhile, the interfacial bonding strength of the composite coating increased from 5.51 N to 7.89 N, and the bonding force increased by 43%. Overall, the surface roughness of MAO coating determined the interface bonding strength with DLC coating. Increasing the surface roughness could significantly improve the interface bonding strength of composite coating, however it would also increase the surface porosity, resulting in the deterioration of corrosion / wear protection performance of MAO coating and its composite coating.