The purpose is to increase the corrosion resistance of magnesium alloy. First, magnesium alloy is pretreatment by micro-arc oxidation craftsmanship, and micro-arc oxidation/hexadecyltrimethoxysilane self-assembled composite coating is drawn up on surface of magnesium alloy by self-assembly machinery. The micro-structure and construction of the composite coating are analyzed by SEM and EDS, and the surface composition of composite coating spectroscopy is analyzed by XPS and Raman. Magnesium alloy composite coating is detected by electrochemical impedance spectroscopy, polarization curve, salt spray test and immersion test corrosion resistance of the coating. The composite coating even provides for the surface of magnesium alloy, and the surface of composite coating is relatively smooth. The composite coating main contains C, O, F, Si and other elements. After self-assembly, the coating changes from hydrophilic to hydrophobic, and the contact angle reaches 145.07°. According to the electrochemical performance evaluation, the composite coating has excellent corrosion resistance, and its Rct value can reach 2.242×106 Ω.cm2, which is to improve by 2 orders of magnitude based on micro-arc oxidation coating; In contrast, the corrosion current density of composite coating is 1.314×10-8 A/cm2, which is 2 orders of magnitude discounted than that of the micro-arc oxide film. After immersion for 120 h, the corrosion current of the composite coating is still 1.061×10-5 A/cm2. There is no obvious corrosion phenomenon after salt spray test for 120 h. Self-assembly technology obviously improves the corrosion resistance of magnesium alloy substrate. The micro-arc oxidation coating also enhances the adhesion of self-assembly coating to magnesium alloy substrate to a certain extent. Because of the hydrophobicity of composite coating, the time that water droplets stay on the surface of the coating is lowered, so it will enormously develop the corrosion protection of the film as the hydrophobicity increases.