Synthesis of carbon nanofibers from V-type pyrolysis flame is a novel method. It needs simple laboratory equipments and normal atmosphere pressure. 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 served as catalyst. The carbon nanofibers were characterized by scanning electron microscope and transmission electron microscope. This study aims to examine temperature condition for carbon nanofibers formation in pyrolysis flame and to characterize its morphology and structure. The carbon nanofibers with less impurity were captured successfully in the V-type pyrolysis flame. The diameter of carbon nanofibers was approximate between 100nm and 200nm, and its length was dozens of microns. When the temperature was below 750°С , the growth of carbon nanofibers came into the preparation growth period. The length of the carbon nanofibers increased gradually and the diameter had no obvious change with the raising of temperature. When the temperature was above 750°C, the growth of carbon nanofibers came into the exuberant growth period. The growth of carbon nanofibers was finished when the temperature was above 820°С . Higher temperature was meaningless after the carbon nanofibers formation. The contrast experiments show that it is the most favorable to form carbon nanofibers when the temperature is from 750°С to 850°С .