Abstract: Several carbon nano-materials,such as nano-graphite, nano-carbon and nano-carbon tube, were used to measure chlorine isotope ratios as an emitter. In this article the measuring time and the observed ion intensity as well as the precision of the gained data by using the three carbon nano-materials to measure the chlorine isotope ratios are compared with that does by using CA graphite, a normal graphite. From these, the study indicates the measured chlorine isotope ratios by using these carbon nano-materials are all higher than that by using CA graphite, but the precisions are all lower than that got by CA graphite. Thus it comes to the conclusion that these carbon nano-materials are not fit for the measurement of the chlorine isotope ratios by positive thermal ionization mass spectrometry.