The understanding of the influence of the deposited dust on the desulfurization performance of sorbent is of significance for developing a combined process for simultaneous desulfurization and dust removal in hot gas cleanup. In this paper, the influence of fly ash from a fluidized-bed coal gasifier on the desulfurization performance of iron oxide sorbent made by a kind of waste material containing iron oxide was systematically evaluated in the temperature range of 400 degreesC to 550 degreesC in a fixed-bed reactor. The results showed that fly ash could interact with the sorbent and adversely influence the sulfur capacity and sulfidation rate of the sorbent. The interaction was promoted with increasing sulfidation temperature and quantity of fly ash. But below 450 degreesC, the interaction becomes negligible. Kinetic studies were conducted using the grain model. Deposition of fly ash on the surface of the sorbent could cause the hindering of mass transfer and the decrease of the effective diffusivities. In addition, the mechanism of influence was discussed. It was found that the reaction of carbon with iron oxide and the sintering of minerals in fly ash with components of sorbent at higher temperature plays an important role in causing the fly ash to be influential.