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, inlet velocity, tube diameter on surface catalytic combustion reaction, and comparison of numerical and experimental studies were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The effect of the surface catalytic reaction on the gas phase reaction can be divided to three types. The existence of catalytic wall will help to reach complete reaction in the micro-tube. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.