Porous magnesium has feature of biodegradation, which will generate an alkaline environment to promote forming of bone tissues. In addition, the porous structure can provide access for new bone growth. So porous magnesium is an ideal bone filling material. Compared with bulk magnesium, the faster degradation rate of porous magnesium will lead to serious alkaline environment surrounding bone tissue, which may induce the osteolysis. To reduce the degradation rate, different surface modification methods are used to match the degradation rate with the healing rate of bone tissues. Based on the research of protective coating of bulk magnesium, and according to the results of previous studies, a new surface modification method for the preparation of micro-arc oxidation and fluorochemical-conversion coating with good effect was selected to reduce the degradation rate of porous magnesium. This paper characterizes the surface morphologies of outer profile and inner pore, cross-section morphology, element composition and thickness of coatings, studies the degradation properties of porous magnesium treated with two kinds of coatings by immersion method, and analyzes the changes of coating morphology, coating elements and coating thickness after immersion, so as to select a better coating treatment method to be more suitable for surface modification of porous magnesium. The fluoride-conversion coating was uniform and density on outer profile and inner pore surface, with the thickness of about 2 μm, the inner pore thickness of the coating was thinner than the outer one; while the micro-arc oxidation coating was porous on outer profile and inner pore surface, with the thickness of about 15 μm, the inner pore thickness of the coating was thinner than the outer one. In addition, the protective effect of the coating prepared by micro-arc oxidation on porous magnesium was relatively stable. Its initial protective effect of the coating on the matrix was slightly worse than that of the fluoride-conversion coating. However, as the immersion time increases, the coating becomes relatively dense, and its protective effect on the porous magnesium matrix becomes more and more obvious. The pH value during degradation of porous magnesium treated by micro-arc oxidation is suitable for bone cell proliferation. Both micro-arc oxidation coating and fluoride-conversion coating could decrease the degradation rate of porous magnesium effectively.