Joint addition of Y and Ce results in excellent ignition-proof effect and realizes no-protection melting in air for magnesium alloys. AES and XRD surface analyses show that an oxidation film mainly composed of Y2O3 was formed on the surface when the Mg-Y-Ce ignition-proof alloys were exposed in air at high temperature. When the Mg-Y-Ce alloys were oxidized at 773, 873 and 973 K in dry air, the oxidation dynamics curves followed the cubic law. Base on the oxidation thermodynamics, the selective oxidation mechanism for Mg-Y-Ce alloys at high temperature was analyzed. The semiconductor characteristics of Y2O3 film and its proof effect on magnesium alloy oxidation were discussed electrochemically