Abstract: The carbon nanotubes were produted by dc arc-discharge method through helium and argon gas respectively at a controlled pressure. The crude nanotubes were oxidized at 770℃ until about 1% of the weight remained and the purified nanotubes were obtained, The electron spin resonance spectrum of purified carbon nanotubes prepared under different inert gases and their pressures have been measured.The dependence of the ESR line shape,linewidth, g vahie of the purified nanotubes on the inert gases and their pressures is found and discussed.