HFC125 gas is an effective ignition-proof protection to high temperature magnesium alloy melt. The surface films from the reaction between HFC125/N2 gas mixture and Mg alloy melt was studied under the weak or strong air convection condition. The results show that under the condition of weak air convection, almost no oxygen ion exists in the obtained surface film, while under the condition of strong air convection, the surface film contains a small amount of oxygen ion. The protection effect does not change obviously for the both working conditions.