<p>Based on first principles, this study has investigated the surface stability and hydrogen evolution reaction (HER) of Mg₁₇Al₁₂ and Mg₂₄Y₅ phases in Mg alloys. The stability of different surface terminations of the Mg₁₇Al₁₂ and Mg₂₄Y₅ phases was evaluated by calculating the surface energy and work function. The stable adsorption sites of H atom on the Mg₁₇Al₁₂ (001) and Mg₂₄Y₅ (001) surfaces were determined by calculating the adsorption free energy of H atom at different sites. In addition, the electron density analysis was used to reveal the influence mechanism of atomic structure distribution on the adsorption behavior of H atom on the second phase surface. The results showed that Mg₁₇Al₁₂ (110) and Mg₂₄Y₅ (110) surfaces were the most stable surfaces, respectively, and Mg₂₄Y₅ phase acted as the anode in the galvanic corrosion process. And the H atom tended to adsorb in the charge dense regions, usually far away from Al atoms or close to Y atoms on the Mg₁₇Al₁₂ (001) or the Mg₂₄Y₅ (001) surface. This behavior was similar to that of the doped Mg (0001) surface, and has the universality of atomic electronegativity affecting H atom adsorption. This revealed the HER mechanism of the second phase in Mg alloys at the atomic scale, providing theoretical guidance for the design of corrosion-resistant Mg alloys.</p>