We present a combined experimental and theoretical study on interfacial structure and thermodynamics in internally oxidized Ag(SnO2)(p) composites. The orientation relation between in situ formed SnO2 particles and the silver matrix was characterized using high-resolution transmission electron microscopy techniques. First-principles energetic calculations were then performed to predict the equilibrium interface structures and corresponding adhesion properties as functions of temperature and oxygen partial pressure. All results were combined to construct the interface-level thermodynamic stability diagram, for guiding the optimal design of internal oxidation parameters.