The objectives of this study were to investigate the characteristics of desulfurization under different experimental conditions and the effects of desulfurization bed fluidized bed combuster installed with the screen. The experimental results were as follows ; First, as the height of fluidized bed combustor becomes higher, the concentrations of $SO_2$ mainly increased and sulfur retion of paper sludge was higher than that of natural limestone. Second, the desulfurzation by natural limestone occurred at in-bed and the desulfurization by paper sludge occurred in the whole of fluidized bed combuster. In addition, we identified calcium sulfate by the analysis of SEM and XRD. Third, screen at splash region increased sulfur retention 2~5%, air velocity and anthracite fraction had a little effect on the sulfur retention.