The species and shapes of impurities in magnesium alloy melt were studied. Floatation Refining method of Magnesium Alloys melt and eduction dynamics analysis were used to judge the floatation condition of gas bubble with MgO impurity. Models of floatation eduction were established to study the dynamics relationship of weight, drag and buoyancy. The relation curve between refining gas bubble radius and floating up rate was established. The choice method of gas bubble radius was provided and a practical process scheme proposed for floatation refining of magnesium alloys melt.