A catalyst with active Co particles was obtained by the calcination of Co/Al layered double hydroxides. With this catalyst, large-scale nitrogen-doped carbon nanotubes (N-doped CNTs) were synthesized by chemical vapor deposition at 850 degrees C under a mixture of methane and acetonitrile. CNTs with different nitrogen contents were prepared by changing the flow rates of methane and acetonitrile. SEM, TEM and Raman spectroscopy were used to investigate the structure of the prepared N-doped CNTs. XPS was used to determine the nature of the chemical bonds of nitrogen in N-doped CNTs. The results show that the prepared N-doped CNTs have a uniform structure and a large amount of N doping.