Medical magnesium and magnesium alloys with good biocompatibility can be absorbed and degraded. Due to the elastic modulus close to that of human bone, medical magnesium and magnesium alloys can effectively alleviate the stress shielding effect, thus becoming ideal body implant materials. In body fluids, the medical magnesium alloys often lead to premature failure of the implant due to faster corrosion rate. Therefore, appropriate surface modification is carried out on magnesium alloy to control the alloy degradation rate and improve biocompatibility. A variety of biodegradable magnesium and magnesium alloy surface modification technologies have been developed for different applications and performance requirements. The most common is the formation of a protective coating on the surface of the magnesium alloy to reduce the direct contact between magnesium and corrosive environments, thereby reducing the corrosion rate. These coatings mainly include degradable polymer coatings and some inorganic coatings. The latest research trends of surface-modified coatings and modification techniques of degradable magnesium alloys in recent years were reviewed, and the modification methods of degradable polymer coatings and inorganic coatings prepared on magnesium and magnesium alloys were explored. The principles of surface modification methods such as anodizing, micro-arc oxidation, ion implantation, sol-gel, plasma spraying, chemical deposition, etc. were briefly introduced and advantages and disadvantages were compared. Finally, the problems of the surface modification coating of degradable magnesium and magnesium alloys in clinical application were put forward and the future development direction was expected.