Using DFT calculations, we investigate mechanisms of the impurity-impurity and impurity-matrix interactions in B/N-doped graphene. Our results have revealed that the impurities interact with each other through the long-range screened Coulomb interaction, and the impurity-matrix interaction is understood from the orbital hybridization. The impurity-induced inter-valley interference only shows a minor modification on the Coulombic impurity-impurity interaction. The B impurity binds more strongly with the matrix than the N impurity. The variation of the Fermi-level energy relative to Dirac point with the itinerant carrier concentration, along with the delocalized distribution of the carriers, indicates the nonlocal doping effect of the impurities. (C) 2014 Elsevier B.V. All rights reserved.