Synthesis of carbon nanotubes from V-type pyrolysis flame is a kind of novel method. It needs more simple equipments. The V-type pyrolysis flame experimental system is introduced. Carbon source is the carbon monoxide and heat source is from acetylene/air premixed flame. Pentacarbonyl iron is acted as catalyst. The sampling time was 5 minutes. This study aims to find the influence rule of hydrogen in synthesis of carbon nanotubes from the V-type pyrolysis flame. Carbon nanotubes with less impurity and high yield were captured successfully in the V-type pyrolysis flame. The diameter of carbon nanotubes was approximate between 10nm and 20nm, and its length was dozens of microns. Hydrogen played extremely important role in the flame synthesis of carbon nanotubes. The effect of hydrogen is to improve the pyrolysis of carbon monoxide and to decompose the carbide on the surface of catalyst particle. The flow or concentration of hydrogen will directly decide the surface roughness of carbon nanotubes from the pyrolysis flame. The carbon nanotubes with "carbon tumour" will appear when the relative flow of hydrogen in the reaction gases is too little. Not only the mass flow of hydrogen is important, but also the ratio of mass flow between carbon monoxide and hydrogen is very important according to the experiment results.