Formation of carbon coils were investigated according to the injection starting stage of an incorporated additive gas (SF 6 ) flow during the overall reaction. Among the different injection stage of SF 6 flow, the initial stage is most effective for the formation of the microsized carbon coils. The formation of carbon coils was also investigated step by step during the reaction. In an early step of the reaction, merely carbon nanofilaments could be observed on the sample. With increasing the reaction time, the formation of the carbon coils was initiated and their densities increased. The double helix geometry of the microsized carbon coils seemed to be developed by the precipitating carbon elements from the spinning catalyst. Based on the close investigating results of the coil head area, the detailed growth mode for the double helix geometry of the microsized carbon coils was proposed and discussed.