A series of bamboo-like CNx nanotubes have been synthesized from pyridine precursor by chemical vapor deposition with bimetallic Fe-Co/gamma-Al2O3 catalyst in the range of 550 similar to 950 degrees C. An unusual predomination of pyridinic nitrogen over graphitic nitrogen has been observed for the CNx nanotubes with reaction temperature below 750 degrees C. The pyridinic nitrogen decreases and the graphitic nitrogen increases with rising reaction temperature. A synergism mechanism of C5N-six-membered-ring-based growth through surface diffusion and vapor-liquid-solid growth through bulk diffusion was accordingly deduced and schematically presented. This mechanism could not only explain our own experimental results, but also understand the CNx-nanotube-related experimental phenomena in the literature, as well as be in accordance with the basic principle of diffusion kinetics. A promising route to the challenging topic for synthesizing regularly arranged C5N or high-N-content CNx nanotubes has also been suggested.