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Summary Metal and alloy phase change materials (PCMs) have played an important role in solar energy storage because of their high thermal storage density and thermal conductivity. However, metals and their alloys, especially Mg alloys, are easily oxidized at high temperatures. In order to overcome this shortcoming, we studied the high‐temperature oxidation performance of phase change heat storage alloys. This research investigated and discussed the effect of adding rare earth element yttrium on the high‐temperature antioxidant process in Mg‐based phase change heat storage alloys in detail. In this research, by adding different contents of Y on the basis of Mg‐Ni‐Zn alloys, the cyclic oxidation kinetics and thermodynamics, oxidation products, oxide layer morphology and structure of Mg‐Ni‐Zn‐Y alloys were investigated. The results indicate that the oxidized Mg‐Ni‐Zn‐Y thermal storage alloys are mainly composed of Mg2Ni, ZnO, Y2O3, MgO, and its eutectic structure. The addition amount of Y is positively correlated with the phase transition temperature. The oxidation of Y to Y2O3 segregates on the grain boundaries, hinders the diffusion process of Magnesium ions, Zinc ions, Nickel ions, and Oxygen ions in the oxide film, and replaces the oxidized Mg and Zn elements, which changes the oxidation mechanism and reduces the oxidation of the alloy. And this research provides a theoretical basis for the application of Mg‐based alloy phase change heat storage materials.