Transition metal dichalcogenides (TMDCs) films are potential two‐dimensional materials for next‐generation optoelectronic and electronic devices. Chemical Vapor Deposition, Atomic Layer Deposition, and Metal‐Organic Chemical Vapor Deposition are usually used for the synthesis of the MoS2 films by taking Mo(CO)6 as precursors. However, the mechanism of adsorption and reaction of Mo(CO)6 on the substrate at the molecular level are hardly to know only by the experiments. In this study, the detailed reactions of Mo(CO)6 on α‐Al2O3(0001) are investigated by density functional theory to demonstrate the growth mechanism of MoS2. It is found that, Mo(CO)6 could form a stable chemical bond with the Al‐1 site on the surface, which has large adsorption energy and charge transfer. The decomposition of Mo(CO)6 into Mo(CO)3 exists in a clear order, with the top carbonyl composing firstly, follow by the two parallel carbonyls. In order to determine the stable model of Mo(CO)3, adsorption energy and DOS are analyzed. The Ead is −5.65 eV and the 4d5 s orbitals of Mo atom overlap with the 2 s2p orbitals of O atom, indicating the new chemical bond is forming in 3O‐Al‐2 model. Finally, the LST/QST (Linear Synchronous Transit/Quadratic Synchronous Transit) method is used to search for transition states of Mo(CO)3 sulfuration reactions with CH3S2CH3, H2S, and S2 respectively. This paper provides a theoretical basis for the experimental preparation of MoS2 and provides research ideas for the general synthesis of TMDCs. [ABSTRACT FROM AUTHOR]