[en] In this study, we report a facile method to obtain air-stable n-type graphene by plasma-enhanced chemical vapor depositing Si₃N₄ film on the surface of graphene. We have demonstrated that the overlying Si₃N₄ film can not only act as the penetration-barrier against H₂O and O₂ adsorbed on the graphene surface, but also cause an effective n-type doping due to the amine groups at the interface of graphene/Si₃N₄. Furthermore, the studies reveal that the Dirac point of graphene can be modulated by the thickness of Si₃N₄ film, which is due to competing effects of Si₃N₄-induced doping (n-type) and penetrating H₂O (O₂)-induced doping (p-type). We expect this method to be used for obtaining stable n-type graphene field-effect transistors in air, which will be widely used in graphene electronic devices.