The structures and properties of the Mg-Gd-Cu lamellar interface are investigated by combining experiments and first-principles study. The lamellar structure has a two-phase interface between Mg2Cu and GdCu. The most stable interface structure is a Gd-Cu terminated interface which has the largest separation energy, the stronger metallic-ionic bond and the lowest interface energy after comparing to other possible structures. This study contributes in several ways to our understanding of the Mg2Cu/GdCu lamellar interface structure and provides a basis for analysis and development in material structure and bonding characterization.