The gasification of sewage sludge in near and super-critical water was investigated in a batch reactor. Results showed that the formation of gaseous products could be intensively affected by temperature. In order to understand the effect of temperature on the development of reaction process and the formation of gaseous products better, the detailed characteristics of solid and liquid products were analyzed by SEM, N-2 adsorption -desorption technique, FTIR, TOC, Ammonia-nitrogen analysis and SPE-GC/MS. The changes in the yield distribution of products and the characteristics of solid and liquid products indicated that organic matters in sewage sludge were almost completely dissolved and hydrolyzed in water at 425 degrees C. The dissolution and hydrolysis products were gasified by reforming and other reactions. The polymerization and dehydrogenation also occurred in dissolution and hydrolysis products, and the Diels-Alder reaction mechanism could be used to explain the phenomenon. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.