Abstract: The combustion characteristics of sludge samples including paper mill sludge, lake sludge and tannery sludge were investigated by using thermogravimetric analysis(TGA). The sludge tested had high volatile, high ash and lower calorific value. The results show that the combustion process of sludge can be divided into two stages. The first stage is the release and combustion of the volatile matter in sludge, and the second is the combustion of the fixed carbon. The weight loss for both combustion of volatile and fixed carbon for tannery sludge is almost equal, while the weight loss by the combustion of volatile accounts for more than 70% of total for lake sludge and paper mill sludge. It is indicated that the main combustible matter in sludge is the volatile matter, and the volatile is combusted in a wide temperature region (from 200℃ to 600℃). The overlapping phenomenon of peaks of the weight loss during the combustion reflects the complexity of the volatile matter in the sludge. Moreover, the reaction kinetics of the combustion of sludge was studied by the integration method of CoatsRedfern.