Comparative analysis of limestone sludge in recycled water and desulfurization limestone is made in the chemical composition, reaction activity, crystallization properties and pH of Slurry. The results show that the limestone sludge in recycled water is possible to be used as a desulfurizer. Due to the large amount of impurities and lower reactivity of limestone sludge, the overall performance index values of limestone sludge are lower than that of desulphurization limestone. If it wants to be used as a desulfurizer, the further research on the using conditions of recycled water limestone sludge in desulfurization system and the possible impact of the reuse of desulfurization system on the stable operation of the system are needed.