Abstract: The equilibrium composition of thiophene hydropyrolysis during steam stimulation was calculated by using the method of multiplier and the concept of minimum Gibbs free energy.The reaction mechanism was analyzed by using laboratory data and equilibrium calculation.The results indicated that hydrolyzation, pyrolysis,hydrodesulfurization, hydrogenation and water gas shift were the main reactions of thiophene hydropyrolysis.When the molar ratio of water to thiophene was less than 4,a higher molar ratio favored both desulfurization and higher gas yield.Only higher gas yield was achieved if the reaction temperature was higher and the pressure was lower.Complete conversion of thiophene could be achieved when the molar ratio of water to thiophene was greater than 4.Temperature,pressure and feed ratio had little effect on the equilibrium composition under this condition.