Abstract: The properties of pyrolysis and combustion for five different sewage sludges are studied by thermal gravimetric analysis at a heating rate of 10℃/min in the atomosphere of nitrogen and oxygen, respectively. The results show that both of the “anaerobic” wastewater treatment and the sludge anaerobic digestion make the organic compounds in sludge so complicated that the organic compounds decomposition and release temperature becomes higher during pyrolyzing, and the “aerobic + anaerobic” process makes the organic compounds in sludge more complicated than the “anaerobic +aerobic” process. There is no influence on the combustion process and the burnout point, but can make the combustion temperature of sludge higher. The thermal reaction mechanisms have been studied with šatava-šesták equation. It shows that the pyrolysis mechanism of these sludges is a process of volatile diffusion at first and then the chemical reaction function, while the combustion mechanism of them is a process of chemical reaction and diffusion function.