Supported sorbent for flue gas desulfurization was prepared by a process of hydrating and drying a mixture of carrier particles and lumps of CaO in previous studies. Supported sorbent achieves high desulfurization efficiency in a Circulating Fluidized Bed (CFB) reactor at moderate temperature. However, the preparation process is complicated, which makes industrial application difficult. In this study, supported sorbent is prepared in situ in a CFB reactor by a coating process, in combination with SO2 removal. The experiments are conducted in a pilot-scale CFB experimental facility at 700-750 degrees C. The influence of operation parameters on supported sorbent formation and desulfurization efficiency is tested, including bed inventory, sprayer location, and spray method. The results show that the present process achieves 85.3% desulfurization efficiency with a Ca/S molar ratio of 2.01 when the bed inventory is 25 kg. This result is approximately 10 times higher than that of a zero bed inventory. The scanning electron microscope and energy dispersive spectrometer results show that the supported sorbent forms when fine Ca(OH)(2) particles in the lime slurry adhere to the bed material surface. The residence time of the supported sorbent in the CFB reactor is significantly longer than that of the fine Ca(OH)(2) particles. The adhesion efficiency is influenced by the spray location and spray method. The desulfurization performance of the supported sorbent prepared by the original hydration and drying method is also tested. The desulfurization efficiency is 25-35% higher than the present process because there is better adhesion in the original method than the in situ method. But the process complexity is significantly reduced when using the present process. The present process is a substantial attempt toward the application of supported sorbent.