Catalytic combustion of hydrogen/air mixture inside micro-tube was numerically investigated with detailed gas phase and surface catalytic chemical reaction mechanisms. Combustion characteristics for different reaction models, the influence of wall thermal conductivity, inlet velocity, and tube diameter on surface catalytic combustion reaction were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The higher wall temperature gradient for low wall thermal conductivity will promote the gas phase combustion shift upstream and will result in a higher temperature distribution. The micro-tube can be divided into two regions. The upstream region is dominated by the surface catalytic reaction and the downstream region is dominated by the gas phase combustion. With increasing inlet velocity, the region dominated by surface catalytic reactions expanded downstream and finally occupied the whole tube. The temperature of the flame core decreases with the decrease of tube diameter. Decreasing the tube diameter will enhance the surface catalytic reactions. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.