Abstract: Synthesis gas (CO + H₂) conversion into clean fuels and chemicals through Fischer-Tropsch Synthesis (FTS) is an important way to clean utilization of coal and ensure China energy security. Investigation of FTS reaction mechanism at the molecular level, including of activation of synthesis gas on catalyst surface, the chain growth via C_nH_x* and C_nH_xO_y*, as well as the chain termination into alkanes, olefins, alcohols, and acids, is the key to the regulation of FTS products, the rational design and development of high-performance catalysts. It is also a hot and difficult point in catalysis science. To study FTS reaction mechanism, intermediate detection, modeling compound addition, steady-state kinetics based on reaction mechanism, steady-state isotope transient kinetic analysis (SSITKA), first-principles calculations, and reaction networks, etc. have been applied to reveal the mechanism of synthesis gas conversion. This paper systematically summarizes the research results of reaction mechanism over the past century, proposes a reasonable route map for FTS reaction, and gives a prospection of the research on FTS mechanism.