The combustion properties of five different sewage sludges were studied by thermal gravimetric analysis in the atmosphere of “oxygen”and “nitrogen + oxygen”, respectively. The results indicate that there are not influence of wastewater treatment process and the sludges anaerobic digestion on the combustion process, but both of the “anaerobic” wastewater treatment and the sludge anaerobic digestion make the ignition temperature of sludge higher, and the temperature of anaerobic digestion sludge is the highest. The relationship among the ignition temperatures of five sludges is independent of combustion atmosphere and heating rate. However, low heating rate makes the temperature of sludge decline. The combustion reaction mechanisms have been studied with Šatava-Šesták equation. It shows that there are the same combustion reaction mechanisms for five sludges in the same atmosphere, and the heating rate hasn’t influence on them, but the combustion atmosphere has influence on them.