In this paper, the effect of Er element on ignition-proof property of Mg-Zn alloys was studied. XRD, SEM and EDS were used to investigate the ignition-proof performance and the oxidation film of the alloys. The element of Er tended to enrich in the surface of molten magnesium alloys during the oxidation process. And the oxidation film was composed of MgO and Er2O3. With the Er content in Mg-Zn alloy increasing, the content of Er2O3 in oxidation film increases and the ignition point of Mg-Zn alloys rise. So Er can improve the ignition-proof properties of Mg-Zn alloys greatly.