The premixed hydrogen/oxygen combustion process in a catalytic micro-combustor was numerically simulated with CFD software. The interaction between gas-phase and catalytic reaction was analyzed by changing inlet parameters on the basis of experimental verification. Meanwhile, the blow-off limits for combustor with and without catalyst were also investigated. The results showed that gas-phase reaction was subdued with the intermediate products consumed in catalytic reaction. At the same velocity, the flame temperature of catalytic combustor was lower than that of non-catalytic combustor. The OH mass fraction near up-wall of Pt cell in catalytic combustion chamber was also lower than that near up-wall of SiC cell in non-catalytic combustor. While owing to the exothermic surface reaction with Pt cell, the temperature of Pt cell in catalytic combustor was higher than that of SiC cell in non-catalytic combustor. Catalytic reaction was dominant near the surface of catalyst, while gas-phase reaction was dominant away from the surface. The OH mass fraction distribution trend near the inner up-wall in catalytic combustor was consistent with that near the inner up-wall in non-catalytic combustor. The blow-off limit can be widened by adding catalyst. The blow-off limits for combustor with and without catalyst were 46 m/s and 22 m/s, respectively. At equivalence ratio of 1.0, the strongest activity of catalytic was shown, and the gas-phase reaction was obviously restrained. With the increase of equivalence ratio, the mean temperature of out-wall was risen at the beginning and then it was dropped later. The highest mean temperature of out-wall was achieved with equivalence ratio of 1.0.