Methyl mercaptan (CH₃SH) is a common sulfide in oil and natural gas, easily corroded in transportation pipes and storage containers. In this paper, the adsorption and dissociation processes of CH₃SH on FeS (0 0 1), (0 1 1), (1 0 0) and (1 1 1) surfaces have been studied by the density functional theory (DFT). And the characteristics of the adsorption and dissociation processes were elucidated. The calculated surface energies show that the order of surface stability is (0 0 1) > (0 1 1) > (1 0 0) > (1 1 1). The stability of CH₃SH adsorption is (1 1 1) > (1 0 0) > (0 1 1) > (0 0 1) by the adsorption energy, and the most stable adsorption configurations are obtained. Compared with the changes in electron density and the partial density of states (PDOS) before and after adsorption, there is an obvious electron orbital hybrid phenomenon between CH₃SH and FeS (1 0 0), (1 1 1) surface, and its adsorption is stronger than that of the other two surfaces. It can be seen from the calculation of the transition state that the dissociation reaction of CH₃SH is endothermic on the (0 0 1) and (0 1 1) surfaces, while the exothermic reaction on the (0 1 1) and (0 0 1) surfaces. CH₃SH will dissociate preferentially on the FeS (1 0 0) surface because the reaction of Ea and ΔE on this surface is the smallest. Overall, the adsorption and dissociation processes are exothermic, the increase in temperature makes the crystal surface unstable and susceptible to spontaneous combustion, and the phenomenon occurs first on the FeS (1 0 0) and FeS (1 1 1) surfaces. These findings increase the understanding of the electronic structure and energy of the sulfides' action on the FeS surface and also have a reference value for flame retardant research.