Epitaxial growth on transition metal surfaces is an effective way to prepare large-area and high-quality graphene.However,the strong interaction between graphene and metal substrates suppresses the intrinsic excellent properties of graphene and the conductive metal substrates also hinder its applications in electronics.Here we demonstrate the decoupling of graphene from metal substrates by germanium oxide intercalation.Germanium is firstly intercalated into the interface between graphene and Ir(111)substrate.Then oxygen is subsequently intercalated,leading to the formation of a GeOx layer,which is confirmed by x-ray photoelectron spectroscopy.Low-energy electron diffraction and scanning tunneling microscopy studies show intact carbon lattice of graphene after the GeOx intercalation.Raman characterizations reveal that the intercalated layer effectively decouples graphene from the Ir substrate.The transport measurements demonstrate that the GeOx layer can act as a tunneling barrier in the fabricated large-area high-quality vertical graphene/GeOx/Ir heterostructure.