Abstract: The combustion of three types of sewage sludges from different municipal wastewater treatment plants was studied by the thermal gravimetric analysis at a heating rate of 30℃/min. Effects of wastewater treatment process and sludge treatment process on the organic compositions and combustion characteristics were discussed. It is observed thatthe anaerobic process can make the organics structure in the sewage sludge so complicated that the higher temperature of combustion is required. Comparative study on pyrolysis in N2 and combustion was done by TGAFTIR analysis. During pyrolysis the sewage sludge decomposes to lower molecular weight volatile compounds. Oxygen can accelerate the decomposition. The pyrolysis temperature of sewage sludge lies in the range of 200℃～500℃. The main gas products include H2O, CO2, CO and hydrocarbons. CO2 is generated not only in the temperature range 200℃～500℃ but also at 750℃ because of the decomposition of inorganic compounds.