The properties of C3N/graphene heterostructures and their electrochemical performance serving as anodes for Li-ion batteries are systematically studied using density functional calculations. Present results demonstrate that C3N/graphene exhibits a metallic behavior, favorable stability and ultrahigh stiffness, which are well maintained even under the applied strains and after lithium adsorption, ensuring the electrode's good electric conductivity and integrity against pulverization. Most particularly, it is predicted that C3N/graphene possesses a maximum Li-storage theoretical capacity of 1079 mA h g−1, low average open-circuit voltages (0.13 V) and Li-diffusion barrier (0.28 eV). These encouraging findings indicate that C3N/graphene heterostructures can be appealing anode materials for Li-ion batteries.