An underfeed circulating spouted bed (UCSB) reactor was used as a desulfurization apparatus. In this study, an attempt was made to build a mathematical 3D model which couples the complicated flow and chemical reactions in the interest of system analysis and sulfur removal data analysis. A simplified reaction model was developed to describe the SO2 absorption process. Humidifying, evaporation, neutralization reaction have been considered in the model while the dissolution and ionization of calcium hydroxide are neglected. The effect of operating parameters including feed style, injecting velocity, jet water flow rate, humidifying style on sulfur removal efficiency were investigated. The results show that the calculation gives a good description of the experimental data under the range of operating conditions. It indicates that the model is successful in predicting the desulfurization efficiency of the UCSB system. (C) 2010 Elsevier B.V. All rights reserved.