To improve the corrosion resistance, bioactivity and bonding strength of magnesium alloys, fluoride doped hydroxyapatite (FHAp) coating was fabricated on micro-arc oxidation (MAO) treated AZ31B magnesium alloy by a simple hydrothermal treatment. The surface morphology, phase composition, electrochemical property, degradation behavior and cytocompatibility of the prepared coatings were investigated in this study. The effect of the doping amount of fluoride ion on the morphology and phase composition of the composited coating was also studied. Through controlling the doping amount of fluoride ions, a uniform and dense FHAp coating composed of many nanorods was successfully prepared on MAO treated AZ31B magnesium alloy. And the the addition of fluoride ions in hydrothermal solution can facilitate the formation of FHAp phase in the coating. The thickness of FHAp/MAO composite coating was about 20 mu m and the coating showed good adhesion to the substrate. And the composite coating showed higher corrosion resistance and lower degradation rate than Ca-P/MAO composite coating and the uncoated substrate. Moreover, osteoblasts cellular tests proved that the FHAp/MAO composite coating significantly improved the cell adhesion and spreading, proliferation and expression of alkaline phosphatase due to the doping of fluoride ion.