The growth of graphene on Ni magnetic films is of great significance for graphene spintronics, whereas the existence of grain boundaries and twin crystal structures in Ni films is an obstacle for obtaining the large-scale and uniform graphene. In this paper, an epitaxial wafer-scale single-crystalline Ni(111) film with the flat and clean surface was successfully prepared on the commercial alpha-Al2O3(0001) substrate by a two-step method, which was demonstrated with several characterization methods. According to the abnormal grain growth mechanism, the clean and uniform sapphire surface plays a key role for the single crystallization of Ni films as it induces a weak interface energy difference between two atomic stacking structures (ABC and ACB), thus stimulating the evolution of Ni films from (111) out-of-plane textures to single crystals. Furthermore, an ultra-flat and wrinkle-free graphene monolayer was synthesized on the prepared Ni film, which further verified its high quality and effectiveness.