The process of sewage sludge steam gasification can be divided into three stages: devolatilization, volatiles homogeneous reforming and heterogeneous catalyzing. This study investigated the direct and indirect impacts of Fe/Ca-based conditioners on syngas generation at different stages using a special decoupling reactor. The results show that the highest H-2 production for raw sludge gasification was 190 mL/g at 1273 K. The maximum promotion of H-2 yield was 51.2% for Fenton's reagent (Fe2++H2O2) addition at 1273 K and 132.5% for CaO addition at 1073 K. Among that, 52.8% and 62.9% of H-2 increment was attributed to the catalytic effect on devolatilization stage respectively. Fenton oxidation was conducive to the conversion and fixation of protein structure while the corresponding organic matter in CaO-conditioned sludge was aromatics. The catalysis of volatile reforming was proven an important process, thus reusing char/ash as bed material or cracking catalysts maybe a promising method for hydrogen energy production. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.