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 helium 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 carbon nanotubes were between 10nm and 20nm in diameter and dozens of microns in length. Helium played extremely important role in the flame synthesis of carbon nanotubes. The effect of helium is to dilute the concentration of combustible and reduce the flame temperature. Hydrogen also can keep the catalyst particles remain active and increase the yield of carbon nanotubes. Too high or low mass flow of helium was not appropriate for the formation of carbon nanotubes in V-type pyrolysis flame. The carbon nanotubes with "carbon tumour" will appear when the flow of helium is too high. Too low flow of helium will reduce the number of carbon nanotubes due to lack of cooling and dilution of the protection gas. It was found that the optimal flow of helium was about 0.283 SLM according to the experimental results.