The　properties　of　BaO/MgO-type　interface　in　the　BaZrO3/MgO(001)　heterostructure　are　studied　by　aberration-corrected　high-resolution　transmission　electron　microscopy　combined　with　first-principles　calculations.　Experimental　evidence　demonstrates　that　cation　displacement　and　vacancies　occur　at　the　interface.　Our　first-principle　calculations　show　that　cation　displacement　results　from　the　electrostatic　potential　effect　at　the　interface,　and　cation　vacancies　could　lower　the　interfacial　work　of　separation　and　enhance　the　interfacial　stability　of　BaO/MgO-type　interface.　The　results　highlight　that　the　effect　of　interfacial　defects　should　be　taken　into　account　in　understanding　the　film　growth　kinetics　and　properties　in　oxide　heteroepitaxy.