The work aims to study the preparation of biodegradable coatings on biomedical magnesium alloys, and characterize their preparation conditions, corrosion resistance, in vitro degradation and cytotoxicity. Firstly, functional monomer 2-methylene-1,3-dioxane (MDO) and 7-(2-methacryloxyethoxy)-4-methyl coumarin (MAC) were synthesized and vinyl acetate (VAc) was selected as copolymers to synthesize degradable polymer P (MAC-VAc-MDO) (PMVO)through free radical ring-opening polymerization. Then, the PMVO polymer was dissolved in dichloromethane and the degradable coatings were prepared on AZ31 magnesium alloy surface via dip-coating. The effects of different preparation conditions (dipping times, concentration and temperature) on the thickness, mass and water contact angle of the coatings were investigated and the optimum preparation conditions were chosen. The polarization curves were utilized to characterize the corrosion resistance of the coatings. The in vitro degradation performance and cell cytotoxicity of the degradable coatings were characterized by simulated degradation experiments and cell experiments. When the dipping times were 3, the concentration of polymer solution was 30 mg/mL, and the temperature was 40 ℃, the coating prepared by dipping method was uniform and compact, and had good corrosion resistance. The simulated in vitro degradation experiments showed that the pH and magnesium ion concentration of the coating sample after immersion decreased compared with the bare magnesium. Cytotoxicity experiment of the extract proved that the degradation products of the coating were non-toxic. The polymer PMVO can be synthesized by free radical ring-opening polymerization and the degradable coatings are prepared on magnesium alloys by dip-coating. The coatings prepared under the optimum conditions have good corrosion resistance, biodegradability and cell cytotoxicity.