We recently developed a micro-combustor with a bluff body, which has a demonstrated 3- to 5-time extension in the blow-off limit. In the present work, the dimension effect of the bluff body on the blow-off limit (indicated by the blockage ratio, zeta) was investigated with a detailed H-2/O-2 reaction mechanism. The results indicate that the blow-off limits for zeta = 0.3, 0.4 and 0.5 are 20, 31 and 36 m/s, respectively. Analyses reveal that for zeta = 0.3, flame blowout occurs due to insufficient recirculation zone size. However, flame blowout occurs due to the stretching effect in the shear layers when zeta = 0.4 and 0.5. Calculations indicate that the three cases have negligible differences in heat loss because the high temperature zones are located in the combustor centers; therefore, their effects on the combustor walls are mitigated. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.