Adding the two-dimensional (2D) material into the metal/oxide interface is a novel method to tune the property of the interface and the interface-controlled device. Compared to the widely studied influence of the interfacial 2D-material on the kinetic diffusion of the atom across the interface, the effect of the interfacial 2D layer on the energetic behavior of the point defect at the interface viewed at the electronic-/atomic-scale is less focused. In this work, the influence of graphene on the Au/HfO2 interface is studied using a first-principles calculation. It is found that graphene can eliminate the Au-induced insulator-metal-transition of the HfO2 layer at the interface, by screening the strong interaction between Au and HfO2. At the atomic scale, graphene significantly increases the formation energy of the oxygen vacancy and vacancy pair in HfO2 at the Au/HfO2 interface, making the interfacial HfO2-layer surface-like. Also graphene alleviates the valence-electron-number dependent segregation of the alloying elements Ag, Cu and Ta at the Au/HfO2 interface. The significant impact of graphene at the metal/oxide interface unraveled from the energetic point of view provides an alternative insight into the interface engineering of the electronic device such as the oxide-based resistive random access memory.