Six-membered-ring-based growth mechanism of carbon nanotubes with benzene precursor was deduced by in situ thermal analysis-mass spectroscopic data and supported by density functional theory calculations.Enlightened by this mechanism, the nitrogen-doped carbon nanotubes with predominant pyridinic N over graphitic N were prepared with pyridine or pentachloropyridine precursor, which present great advantages in the facile construction of various nanocomposite electrocatalysts for fuel cells.