The combustion and flow characteristics of H-2/O-2 mixture were numerically studied in a platinum-coated planar channel with a length of 20 mm and a height of 1 mm. Two-dimensional numerical models were built and verified by experimental data. The fundamental of generating unstable combustion and flow and its influencing factors were studied via changing the parameters (equivalent ratio, initial position of reaction, with or without homogeneous reaction). It was found that pure heterogeneous reaction could affect the flow state in the planar micro combustor because of the intense convective heat transfer on the inner wall. The critical Reynolds number in micro combustor calculated by pure heterogeneous reaction model was in the range of 650-1100. The reaction heat of catalyst surface and the thickness of boundary layer at the initial position of heterogeneous reaction are two main factors which influenced the stability of combustion and flow. Finally, the pure heterogeneous reaction had higher complete combustion efficiency than coupling reaction. Based on these conclusions, the applicable conditions for achieving stable flow and combustion in the microchannel were obtained, which could provide a theoretical basis for the application in micro-combustion. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.