Heteroatom-doped carbon has been extensively investigated as metal-free electrocatalysts to replace commercial Pt/C catalyst for oxygen reduction reaction (ORR) in fuel cells and Li-air batteries. However, the synthesis of heteroatom-doped carbon could not be easily realized. In this work, TCNE as a small molecule with strong electron-accepting ability was used to functionalize graphene (Graphene-TCNE) as efficient metal-free electrocatalysts for ORR. The charge transfer process was observed from graphene to TCNE by X-ray photoelectron spectroscopy and Raman characterizations. Our DFT calculation found that the as-observed charge transfer behaviour from graphene to TCNE could alter the electron and spin density of carbon atoms in the graphene plane, which further enhanced the electrocatalytic activity towards ORR. Unlike the synthesis of heteroatoms-doped carbon electrocatalysts, the preparation of TCNE functionalized graphene is very simple and available for large-scale applications. The strategy developed here provides a novel and facile approach to the design of carbon-based metal-free electrocatalysts.