Combustion characteristics of H-2/air mixture in a micro-combustor with wall cavities were investigated numerically. The effects of inlet velocity, equivalence ratio, and the length-depth ratio of the cavity were studied. The results show that at a high enough velocity the flame splits in the middle which leads to a large amount of fuel leakage and a sharp decrease in the conversion rate of hydrogen. Meanwhile, the flame splits at the inner wall which gives rise to two high temperature regions and double temperature peaks at outer wall. Moreover, the flame-splitting limit is extended at a higher equivalence ratio due to a more intensive reaction. Furthermore, the flame-splitting limit increases for a larger length-depth ratio of the cavity, whereas the wall temperature level decreases. Therefore, excessive large length-depth. ratios are not beneficial for this type of micro-combustors if the combustor walls are used as heat sources of thermoelectric or thermal photovoltaic devices. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.