Due to good biocompatibility and degradability, magnesium alloy has become a key research object in the development of coronary stents and other medical devices. There is a problem to limit the biomedical application of magnesium alloy for too fast degradation rate. In order to improve the corrosion resistance of magnesium alloys, different protection technologies have been proposed such as chemical composition, microstructure and surface modification, mainly including alloying, anodizing, micro-arc oxidation, electrodeposition and superhydrophobic coating. The superhydrophobic coating is a method that significantly improves corrosion resistance by constructing an insulating layer to reduce the contact area and contact time between the corrosive medium and the substrate material. A superhydrophobic surface modification of magnesium alloy will be carried out to reduce the degradation rate of magnesium alloy and platelet adhesion. In order to improve the anti-corrosion property of AZ31B magnesium alloy and obtain better hemocompatibility, a superhydrophobic coating was scrapped on magnesium alloy with polydimethylsiloxane by Meyer rod and sieved silica particles. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the coating and SEM-EDS mapping was used to analyze its surface element distribution. The characteristic peaks of the composite coating were characterized by infrared spectroscopy to determine their chemical structure. The contact angle measuring instrument was used to test the hydrophobicity of the coating. The anti-corrosion performance of composite coating on magnesium alloy was tested through electrochemical testing. Hemocompatibility was analyzed by in vitro platelet adhesion and hemophorecity test evaluation. The SEM images showed that the composite coating prepared by the scraping was a uniform and dense form on the surface of AZ31B magnesium alloy. The PDMS/H-SiO2 composite coating surface presented a micron-scale particle under high magnification. The rough morphology helped to form superhydrophobic surface. The coating including silicon, oxygen and carbon elements could be known through EDS data. The infrared spectroscopy results confirmed that the composition of composite coating was PDMS and SiO2. After soaking in 3.5wt.% sodium chloride solution, compared with the control group of bare AZ31B magnesium alloy and PDMS-only coated magnesium alloy, the capacitance of composite coating (1.56 × 10?7 F/cm2) was the minimum value and the resistance (2.85 × 106 Ω.cm2) and charge transfer resistance (5.69 × 106 kΩ.cm2) were the maximum values. The corrosion current density of the composite coating was reduced by five orders of magnitude compared with that of the magnesium alloy, and the corrosion voltage was positive. In conclusion, excellent corrosion resistance was shown by corrosion inhibition efficiency of 99.99%. Additionally, there were no adherent platelets on the surface of the composite coating, and the blood contact angle was greater than 150°, showing super-hydrophobicity. In summary, a simple and excellent superhydrophobic composite coating is prepared to improve the corrosion resistance of magnesium alloys. The composite surface exhibits superhydrophobicity and excellent hemocompatibility. It provides a new anti-corrosion strategy for broadening the application of magnesium alloys.