A new process of flue gas desulfurization in circulating fluidized bed with flue gas bypass ducts is presented. k-epsilon Model, Discrete Phase Model and Finite-Rate Chemistry Model are proposed to simulate the desulfurization process characteristics in circulating fluidized bed reactor. The proposed model is validated by the comparison of experimental data and simulation results. The results show that the desulfurization reactor with bypass ducts is superior to the reactor without bypass ducts. The reactor with bypass ducts has higher desulfurization efficiencies and lower flow resistances than the reactor without bypass ducts, and it is more suitable for flue gas flow variation. Desulfurization reaction rate is controlled by absorption reaction on sorbent particles surface. When water content and Ca/S ratio increase, desulfurization efficiency of the reactor with bypass ducts increases. When SO2 concentration increases, desulfurization efficiency decreases. (c) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.