Abstract: Thermodynamics of poisoning on F-T synthesis catalyst with carbonyl sulfide were calculated according to some thermodynamic data and related software. Poisoning of Ru, Fe and Co can occur spontaneously under the conditions of F-T synthesis reaction because of the low negative value of ΔG thermodynamically. Ruthenium in Ru-based F-T synthesis catalyst can be poisoned by the COS on 10^-9 level. There are many types of Fe and Co sulfide generated in the poisoning reactions. Their equilibrium constants are much different for different reactions, and their necessary concentrations of COS are also different. As the active phases of the Fe-based F-T synthesis catalyst are complex, it is feasible to develop some sulfur resistant catalysts. And for the Co catalyst, the characteristics of F-T synthesis reaction and the modification of catalysts may contribute to the development of sulfur tolerant catalyst possibly.