The Fischer-Tropsch synthesis (FTS) has become an attractive industrial process to produce fuels and chemicals from coal, natural gas and biomass. It has also been invoked to explain the formation of abiogenic hydrocarbons in the Earth’s crust, the formation of organic matters in the nebula, and the production of precursors of life-essential building blocks. The question of how the long chain hydrocarbons are formed from two simplest compounds CO and H2 is of fundamental importance in chemistry and has challenged researchers for many years. The key to understand the mechanism of the FT reaction is to know how the C-C bonds being formed from surface growing chains and the monomer. Even though the structures of growing chains and monomer are still not known, many possible structures have been proposed by analogy with organic compounds. The simplest surface growing chain is the surface C2 species that is formed from monomers by C-C coupling promoted by metal catalyst. If we know how the C2 species is formed, we will have a clear picture about the formation of longer chain hydrocarbons. Therefore, one of the most important tasks in studying mechanism for the FT reaction is to study C2 surface species. There are at least four possible C2 structures as shown in Figure 1, each of which corresponds to a different mechanism for the FT reaction: the structure I, the hydroxyl methylene mechanism proposed in 1951 by Storch and co-workers; the structure II, the alkyl mechanism proposed in 1980 by Brady and Pettic; the structure III, the alkenyl mechanism proposed in 1995 by Maitlis and co-workers; the structure IV is corresponding to the modified alkylidene mechanism proposed by us in 2011 [1,2].