The reaction mechanisms of metal hydrides in the combustion of solid propellants are closely related to their effects on the energetic and combustion properties of propellants. Here, we report a first attempt to investigate the reaction mechanisms of ZrH2, a promising candidate for fuels, in the combustion of HTPB propellants using ammonium perchlorate (NH4ClO4, AP) as the oxidizer. ZrH2 is determined to possess a good resistance to the direct oxidation by AP. Thus, it would dehydrogenate independently to generate H-2 and metallic Zr, which is believed to be very favorable for decreasing the gaseous molecular masses. On the other hand, due to the attachment of gaseous reactants to it, ZrH2 was found to tune the decomposition behaviors of AP by enhancing the generation of NO in the high-temperature decomposition stage. More interestingly, the hydrogen released from ZrH2 is evaluated to promote the combustion reactions in gaseous phases and be responsible for the two-stage combustion behaviors of the corresponding propellant, which are distinct from those when metallic Al is used as the fuel. The findings in this work validate the potential of ZrH2 as a fuel for high-energy solid propellants. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.