Carbon nanofibers synthesis from the flame is a new method. The method needs simple laboratory equipments and normal atmosphere pressure. The experimental system is introduced. Carbon source is the carbon monoxide and the nitric acid nickel is served as catalyst. The carbon nanofibers were characterized by scanning electron microscope and transmission electron microscope. Carbon nanofibers with less impurity were captured successfully in the flame. The diameter of carbon nanofibers was approximate from one to two hundred nanometers, and its length was dozens of microns. The growth process and mechanism of carbon nanofiber from the flame is very complicated. The influence of catalyst can reveal the growth mechanism of carbon nanofiber. This study aims to examine the catalyst formation condition for carbon nanofibers in pyrolysis flame and to characterize the morphology. Carbon nanofibers with less impurity can be prepared when the diameter of catalyst in is between twenty and thirty nanometers. The catalyst particle size can determine the morphology of carbon nanofibers.