Abstract: During the coal pyrolysis with the coal ash as heat carrier, the interactions of coal ash and volatile matters could occur in the secondary reactions, which would affect the final sulfur-containing product yields of volatile matter. The objective of this paper was to reveal the effects of coal ash on the sulfur transformation during the secondary reactions. The results showed that the presence of XLT ash during secondary reactions inhibited H₂S and COS release at low temperatures due to the sulfur fixation of Fe₂O₃ existed in the ash. However, it enhanced H₂S and COS release at high temperatures, which was mainly caused by the formation of sulfur-containing gases through the reactions between CaSO₄ and reducing gas (i.e. H₂, CO, and CH₄). The influences of Fe₂O₃ and CaSO₄ were also investigated to reveal the mechanism of the influence of coal ash, and it was found that H₂S and COS yields were reduced with the addition of Fe₂O₃, but those two gases were slightly increased by the presence of CaSO₄ at 800 ℃, indicating that Fe₂O₃ and CaSO₄ played important roles in the interactions between the coal ash and sulfur-containing gases.