Accurate determination of the bond dissociation energies (BDEs) of large alkanes is desirable but practically impossible due to the expensive cost of high-level ab initio methods. We developed a two-layer ONIOM-CCSD(T)/CBS method which treats the high layer with CCSD(T) method and the low layer with DFT method, respectively. The accuracy of this method was validated by comparing the calculated BDEs of n-hexane with that obtained at the CCSD(T)-F12b/aug-cc-pVTZ level of theory. On this basis, the C-C BDEs of C-6-C-20 n-alkanes were calculated systematically using the ONIOM [CCSD(T)/CBS(D-T): M06-2x/6-311++G(d,p)] method, showing a good agreement with the data available in the literature. (C) 2018 Elsevier B.V. All rights reserved.