We proposed a new model for estimation of the overall rate constant of pyrolysis of n-alkanes at a low conversion level. The model was based on the Kossiakoff and Rice theory, that is, including the following five elementary reactions: initiation, isomerization, β scission, H abstraction, and termination. The carbon number dependence of the rate constant of bimolecular reactions (H abstraction and termination) was taken into account in the model. The model can predict the overall rate constant of n-alkanes (n-C3-n-C32) at a wide range of temperatures (572-973 K) and concentrations (6.86 × 10-3-2.72 M) successfully. Finally, we could explain the carbon number dependence of the overall rate constant of n-alkane pyrolysis from the literature by the theoretical basis.