The Ni-Mg-O compound oxide catalyst and pilot scale fluidized bed reactor were used to prepare carbon nanotubes by catalytic pyrolysis of methane.Effect of main operation variables were studied，which could change the conversion rate of methane，carbon product rate of catalyst，rate of reunited product and loss rate of catalyst. Appropriate conditions were determin ed as follows: inlet velocity of methane was 16~19 cm/s，particle size of catalyst was 150~220 μm，dosage of catalyst was 50~60 g， reaction temperature was 650~700 ℃ and reaction time was 120~140 min.Multiple batches of repeated experiments results show ed that the conversion rate of methane was about 30% and the carbon product rate of catalyst was about 10 gCNTs/g CAT under the selected conditions.SEM and TEM morphological characterization of the purified products showed that the prepared carbon nanotubes had uniform diameter and obvious hollow structure，with outer diameter of 10~30 nm and inner diameter of 2~5 nm.