Surface properties are significantly important to the high capacity and rate capability of LiFePO4 nanoparticles as cathode materials for lithium ion batteries. Using the first-principles total energy calculations, the stability and the electronic structure evolution of the graphene/LiFePO4 interface with different amounts of Li atoms inserted have been systematically investigated. It is revealed that the interfacial Li atom insertion could contribute markedly to the capacity of graphene modified or coated LiFePO4 with large specific interface area. The interfacial binding between graphene and LiFePO4 surface in parallel orientation becomes stronger with the increase of the interfacial Li atoms amount which involves more than van de Waals interaction. The electronic conductivity of the LiFePO4 surface is weakened during the Li insertion at the interface, while the Mn-doped LiFePO4 surface maintains the excellent conductivity in the early stage of lithiation. However, stable polaron forms at the semiconducting LiFePO4 surface during lithiation. Moreover, the graphene modification and the Mn doping exert positive effect on the surface oxygen stability.