A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 degrees C exhibited maximum H-2 yield (7.76 mol kg(-1) dry basis wet sludge) and dry gas yield (0.61 Nm(3) kg(-1)) and H-2 content of 42.13 vol%. When the moisture exceeded 43.38%, H-2 yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H-2 yield and H-2 content were increased from 1.83 mol kg(-1) dry basis wet sludge and 16.67 vol% to 9.15 mol kg(-1) dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 degrees C to 850 degrees C. LHV of fuel gas varies from 15.49 MJ Nm(-3) to 11.65 MJ Nm(-3) because of decrease in CH4 and C2H4 content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.