Gaseous emission of the combustion of two types of representative Chinese sewage sludge (SS) with different moisture content was researched in a circulating fluidized bed combustor. Desulfurization and dechlorination characteristics of limestone and the effect of phosphorus in the sludge on desulfurization were investigated. The results showed that the concentrations of NO, SO2, and HCl increased as the combustion temperature increased, while N2O emission reduced. Air staging had a limited effect on the emissions of nitrogen oxides, especially for NO. Increasing sludge moisture content led to a substantial increase in the emissions of N2O and HCl and a decrease in NO emission. It was found that during sewage sludge combustion the emissions of nitrogen oxides were higher but the fuel-N conversion ratio was lower than those in coal combustion. The fuel-S conversion ratio was between 89% and 95%, while the fuel-Cl conversion ratio was between 39% and 48% for Qinghe SS without limestone injection. Phosphorus content in the sludge had obvious influence on desulfurization. Phosphorus interfered with the self-desulfurization of the fuel and the desulfurization of limestone due to the reaction between phosphoric oxide and calcium oxide.