AM50 magnesium alloys were treated by micro-arc oxidation in a solution containing silicate,potassium fluoride,glycerol and potassium hydroxide at a constant applied anodic current density. Influences of different cathode current density on anodic voltage and micro-morphology,micro-hardness,thickness of coating were investigated at a constant anodic current density. The results indicate that anodic voltages corresponding to different cathode current densities exhibit firstly rapidly increase and then tend to be stable with increasing in time,while it shows firstly increase and then gradually decrease with increasing in cathode current density. In addition,with the increase of cathode current density,the number of micro-pores in the MAO coatings is firstly decreased and then increased,however micro-pore diameters are in range of 1⁵ μm,exhibiting slightly change in size. It is beneficial for increasing micro-hardness and thickness of the MAO coating with increasing in cathode current density.