Oxide heterointerfaces with broken translational symmetry offer a fertile ground for exploring fascinating physical properties that are absent in bulk constituents. Here, we apply advanced transmission electron microscopy to the Sr2FeTaO6/SrTiO3 interface and elucidate that the deposited Sr2FeTaO6 thin film bonds directly to the SrTiO3 substrate in an epitaxial, coherent, and atomically abrupt way. Combined with density-functional-theory calculations, we determine the explicit interface atomistic structure, the exact valence state of transition metals, the covalent interfacial bonding nature, and identify the antiferromagnetic superexchange magnetic coupling path between Fe ions as Fe-O-Ta-O-Fe.